git-applymbox: Remove command

git-applymbox: Remove command

I believe noone uses git-applymbox, and noone definitely should, since it
is supposed to be completely superseded and everything by its younger
cousin git-am. The only known person in the universe to use it was Linus
and he declared some time ago that he will try to use git-am instead in his
famous dotest script.

The trouble is that git-applymbox existence creates confusing UI. I'm a bit
like a recycled newbie to the git porcelain and *I* was confused by
git-applymbox primitiveness until I've realized a while later that I'm of
course using the wrong command.

Signed-off-by: Petr Baudis <pasky@suse.cz>
Signed-off-by: Junio C Hamano <junkio@cox.net>