Problem: The command line takes up space even when not used.
Solution: Allow for 'cmdheight' to be set to zero. (Shougo Matsushita,
closesvim/vim#10675, closesvim/vim#940)
https://github.com/vim/vim/commit/f39cfb72629f3e7fefaf578a3faa2619cd0654f8
Omit win_redr_ruler() change: winbar may still need redraw.
Omit win_update() changes: Nvim doesn't use `Rows` there.
Omit redraw_asap(): removed.