Revert "Use 'setfiletype' to set local &filetype (#473)"

This reverts commit 653cc4d.

Author: jbodah

ftdetect/elixir.vim

@@ -1,9 +1,9 @@
-au BufRead,BufNewFile *.ex,*.exs setfiletype elixir
-au BufRead,BufNewFile *.eex setfiletype eelixir
+au BufRead,BufNewFile *.ex,*.exs set filetype=elixir
+au BufRead,BufNewFile *.eex set filetype=eelixir
 au BufRead,BufNewFile * call s:DetectElixir()
 
 function! s:DetectElixir()
   if &filetype !=# 'elixir' && getline(1) =~# '^#!.*\<elixir\>'
-    setlocal filetype=elixir
+    set filetype=elixir
   endif
 endfunction