vim: Move numbertoggle autocmd into settings.vim

Step by step I want to restructure the vim files. The approach to
cleanly divide the config by topics works in zsh pretty well, but is too
vague in vim for my liking.

Especially (the very small) functions and autocommands that have the
purpose of setting options or mapping keys or the interplay of multiple
categories together, make it difficult to decide in which file the
snippets should lay.

.config/vim/vimrc.d/80-autocommands.vim

@@ -57,9 +57,3 @@ augroup highlight_current_word
 	au CursorHold * :exec 'match CursorColumn /\V\<' . escape(expand('<cword>'), '/\') . '\>/'
 	au CursorMoved * :exec 'match'
 augroup END
-
-augroup numbertoggle
-	au!
-	au BufEnter,FocusGained,InsertLeave,WinEnter * if &nu | set rnu   | endif
-	au BufLeave,FocusLost,InsertEnter,WinLeave   * if &nu | set nornu | endif
-augroup END