Remove dead links from free-programming-books-langs.md (#10000)

* Remove dead links from free-programming-books-langs.md

* Remove empty section 'Cilk'

* Remove empty section 'Cilk'

books/free-programming-books-langs.md

@@ -33,7 +33,6 @@ Books on general-purpose programming that don't focus on a specific language are
 * [C++](#cpp)
 * [Carbon](#carbon)
 * [Chapel](#chapel)
-* [Cilk](#cilk)
 * [Clojure](#clojure)
 * [CMake](#cmake)
 * [COBOL](#cobol)
@@ -336,7 +335,6 @@ Books on general-purpose programming that don't focus on a specific language are
 * [PC Assembly Language](http://pacman128.github.io/pcasm/) - P. A. Carter
 * [Programming from the Ground Up](https://download-mirror.savannah.gnu.org/releases/pgubook/ProgrammingGroundUp-1-0-booksize.pdf) - Jonathan Bartlett (PDF)
 * [Ralf Brown's Interrupt List](http://www.ctyme.com/rbrown.htm)
-* [Run Down On x86 Intel Assembly Course](https://github.com/Ret2LC/x86-assembly) - Ret2LC
 * [Software optimization resources](http://www.agner.org/optimize/) - A. Fog
 * [The Art of Assembly Language (2003)](https://web.archive.org/web/20120525102637/http://maven.smith.edu/~thiebaut/ArtOfAssembly/artofasm.html) - Randall Hyde (PDF) *(:card_file_box: archived)*
 * [The Grain Docs](https://grain-lang.org/docs/)
@@ -352,7 +350,6 @@ Books on general-purpose programming that don't focus on a specific language are
 
 * [Beginners Introduction to the Assembly Language of ATMEL-AVR-Microprocessors](http://www.avr-asm-download.de/beginner_en.pdf) - Gerhard Schmidt (PDF)
 * [Easy 6502](http://skilldrick.github.io/easy6502/) - Nick Morgan
-* [Machine Code for Beginners [Z80 and 6502 CPUs]](https://usborne.com/browse-books/features/computer-and-coding-books/) - Lisa Watts, Mike Wharton (PDF) *(scroll to bottom and click on book cover)*
 * [Machine Language for Beginners](https://archive.org/details/ataribooks-machine-language-for-beginners) - Richard Mansfield
 * [MIPS Assembly Language Programming Using QtSpim](http://www.egr.unlv.edu/~ed/MIPStextSMv11.pdf) - Ed Jorgensen (PDF)
 * [Programmed Introduction to MIPS Assembly Language](http://chortle.ccsu.edu/AssemblyTutorial/index.html) 
@@ -564,14 +561,8 @@ Books on general-purpose programming that don't focus on a specific language are
 * [Chapel Tutorial for Programmers](http://web.archive.org/web/20150310075109/http://cs.colby.edu/kgburke/?resource=chapelTutorial) *(:card_file_box: archived)*
 
 
-### Cilk
-
-* [Cilk 5.4.6 Reference Manual](https://par.tuwien.ac.at/material/manual-5.4.6.pdf) (PDF)
-
-
 ### Clojure
 
-* [A Brief Beginner’s Guide To Clojure](http://www.unexpected-vortices.com/clojure/brief-beginners-guide/)
 * [Clojure](https://clojure-book.gitlab.io) - Karthikeyan A K
 * [Clojure - Functional Programming for the JVM](http://java.ociweb.com/mark/clojure/article.html) - R. Mark Volkmann
 * [Clojure by Example](https://kimh.github.io/clojure-by-example/) - Hirokuni Kim
@@ -774,7 +765,6 @@ Books on general-purpose programming that don't focus on a specific language are
 ### Force.com
 
 * [Apex Workbook](https://web.archive.org/web/20170102233924/https://resources.docs.salesforce.com/sfdc/pdf/apex_workbook.pdf) (PDF) *(:card_file_box: archived)*
-* [Developer Workbooks](http://developer.force.com/workbook)
 * [Force.com Fundamentals](http://developerforce.s3.amazonaws.com/books/Force.com_Fundamentals.pdf) (PDF)
 * [Force.com Platform Fundamentals: An Introduction to Custom Application Development in the Cloud](http://www.lulu.com/shop/salesforcecom/forcecom-platform-fundamentals/ebook/product-17381451.html)
 * [Force.com Workbook](https://web.archive.org/web/20160804055738/http://resources.docs.salesforce.com:80/sfdc/pdf/forcecom_workbook.pdf) (PDF) *(:card_file_box: archived)*
@@ -790,7 +780,6 @@ Books on general-purpose programming that don't focus on a specific language are
 * [A Beginner's Guide to Forth](https://web.archive.org/web/20180919061255/http://galileo.phys.virginia.edu/classes/551.jvn.fall01/primer.htm) - J.V. Noble *(:card_file_box: archived)*
 * [And so Forth...](http://ficl.sourceforge.net/pdf/Forth_Primer.pdf) (PDF)
 * [Easy Forth](https://skilldrick.github.io/easyforth/) - Nick Morgan (HTML)
-* [Programming Forth](http://www.mpeforth.com/arena/ProgramForth.pdf) (PDF)
 * [Starting Forth](http://home.iae.nl/users/mhx/sf.html)
 * [Thinking Forth](http://thinking-forth.sourceforge.net)
 * [Thoughtful Programming and Forth](http://www.ultratechnology.com/forth.htm)
@@ -803,8 +792,7 @@ Books on general-purpose programming that don't focus on a specific language are
 * [Fortran 90 Tutorial](https://web.stanford.edu/class/me200c/tutorial_90/) - Sarah T. Whitlock, Paul H. Hargrove, Stanford University (HTML)
 * [Fortran information & resources](https://www.fortranplus.co.uk/fortran-information/) - fortranplus.co.uk (HTML)
 * [FORTRAN Performance Tuning co-Guide (1998)](https://www.ibiblio.org/pub/languages/fortran/unct.html) - Timothy C. Prince (HTML)
-* [Introduction to Fortran](https://qc2-teaching.readthedocs.io/en/latest/programming.html) - Sebastian Ehlert, Julius Stückrath, Marcel Mueller, Marcel Stahn (HTML)
-* [Modern Fortran in Science and Technology](https://modern-fortran-in-science-and-technology.readthedocs.io/en/latest) - Jonas Lindemann, Ola Dahlblom (HTML, [PDF](https://modern-fortran-in-science-and-technology.readthedocs.io/_/downloads/en/latest/pdf/), [EPUB](https://modern-fortran-in-science-and-technology.readthedocs.io/_/downloads/en/latest/epub/))
+* [Modern Fortran in Science and Technology](https://modern-fortran-in-science-and-technology.readthedocs.io/en/latest) - Jonas Lindemann, Ola Dahlblom
 * [Modern Fortran Tutorial](https://masuday.github.io/fortran_tutorial/) - Yutaka Masuda (HTML)
 * [Professional Programmer’s Guide to Fortran77 (2005)](https://www.star.le.ac.uk/~cgp/prof77.pdf) - Clive G. Page (PDF)
 * [Self Study Guide 2: Programming in Fortran 95](http://www.mrao.cam.ac.uk/~rachael/compphys/SelfStudyF95.pdf) - Dr Rachael Padman (PDF)
@@ -827,7 +815,6 @@ Books on general-purpose programming that don't focus on a specific language are
 * [Effective Go](https://golang.org/doc/effective_go.html)
 * [Essential Go](https://www.programming-books.io/essential/go/) - Krzysztof Kowalczyk, StackOverflow Contributors
 * [Go 101](https://go101.org/article/101.html) - [@TapirLiu](https://twitter.com/TapirLiu)
-* [Go Bootcamp](http://www.golangbootcamp.com/book) - Matt Aimonetti
 * [Go by Example](https://gobyexample.com)
 * [Go for Javascript Developers](https://github.com/bulim/go-for-javascript-developers)
 * [Go for Python Programmers](https://golang-for-python-programmers.readthedocs.io/en/latest) - Jason McVetta (HTML, PDF, EPUB)