contrib: remove "emacs" directory

While the "emacs/" directory still exists, all of its code has been
replaced with stubs in 6d5ed48 (git{,-blame}.el: remove old
bitrotting Emacs code, 2018-04-11). Instead, the recommendation is to
use Emacs' own vc-annotate mode.

Remove the code altogether.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t