Remove unnecessary auto-mode-alist additions

The default auto-mode-alist already has an entry that will use c++mode
for .cxx and hpp files.

("\\.[ch]\\(pp\\|xx\\|\\+\\+\\)\\'" . c++-mode)

contrib/lang/c-c++/packages.el

@@ -35,8 +35,6 @@
     (add-to-list 'auto-mode-alist '("\\.h$" . c++-mode))
     :config
     (progn
-      (add-to-list 'auto-mode-alist '("\\.cxx$" . c++-mode))
-      (add-to-list 'auto-mode-alist '("\\.hpp$" . c++-mode))
       (require 'compile)
       (c-toggle-auto-newline 1)
       (evil-leader/set-key-for-mode 'c-mode