updated book-bn - removed a book Because that website does not exist … (#6870)

* updated book-bn - removed a book Because that website does not exist right now

* Fixed issue and  updated book-bn - removed a book Because that website does not exist right now

* replace the broken link with an archive.org link

* replace the broken link with an archive.org link -2

books/free-programming-books-bn.md

@@ -43,7 +43,7 @@
 
 ### Misc
 
-* [SL3 Framework - Code For Brain](https://sl3.app) - Stack Learners
+* [SL3 Framework - Code For Brain](https://web.archive.org/web/20201024204437/https://sl3.app) - Stack Learners *(:card_file_box: archived)*
 * [ডেভসংকেত: বাংলা চিটশিটের ভান্ডার](https://devsonket.com) - Devsonket Team