Merge pull request #917 from Pythagory/master

Remove High Performance Drupal - Not Free

free-programming-books.md

@@ -1290,7 +1290,6 @@ See also [TeX](#tex)
     * [Laravel 4 Official Documentation. Synced Daily](https://leanpub.com/l4)
     * [Official Documentation (Offline Version)](https://leanpub.com/l4-offline-doc)
 * Drupal Framework
-    * [High Performance Drupal](http://chimera.labs.oreilly.com/books/1230000000845) - Jeff Sheltren, Narayan Newton, and Nathaniel Catchpole
     * Drupal 7
         * [The Tiny Book of Rules](https://drupal.org/files/tiny-book-of-rules.pdf) (PDF)
         * [Master Drupal in 7 hours](http://dl.dropboxusercontent.com/u/54624702/Master%20Drupal%20in%207%20hours_v1.1.pdf) (PDF)