MAINTAINERS: adjust to livepatch .klp.arch removal

Commit 1d05334d ("livepatch: Remove .klp.arch") removed
arch/x86/kernel/livepatch.c, but missed to adjust the LIVE PATCHING entry
in MAINTAINERS.

Since then, ./scripts/get_maintainer.pl --self-test=patterns complains:

  warning: no file matches  F:  arch/x86/kernel/livepatch.c

So, drop that obsolete file entry in MAINTAINERS.

Fixes: 1d05334d

 ("livepatch: Remove .klp.arch")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>