Fix :enew handling (again)

fugitive is run at VimEnter and for new buffers that are associated with
files.

Now fugitive commands will be available after start (in the Startify screen),
but it won't work after calling :Startify, since fugitive is designed that
way.

References #33.

autoload/startify.vim

@@ -50,7 +50,6 @@ function! startify#insane_in_the_membrane() abort
     endfor
   endif
 
-  enew
   setlocal
         \ bufhidden=wipe
         \ buftype=nofile