Remove unneeded variable setting.

The variable is script local to autoload/vundle/scripts.vim since #468.

autoload/vundle.vim

@@ -64,7 +64,6 @@ func! vundle#rc(...) abort
   let g:bundle_dir = len(a:000) > 0 ? expand(a:1, 1) : expand('$HOME/.vim/bundle', 1)
   let g:updated_bundles = []
   let g:vundle_log = []
-  let g:vundle_changelog = ['Updated Plugins:']
   call vundle#config#init()
 endf