Close sync result buffer with keybind

[Thaodan]

It would be very handy to kill the buffer similar as to similar buffer such as the Warnings buffer.

[jackkamm]

I agree this would be good. Probably, we should have a mode for org-caldav message and warnings buffers, that derives from special-mode: https://www.gnu.org/software/emacs/manual/html_node/elisp/Basic-Major-Modes.html That way, q will be bound to quit-window automatically. PRs welcome...