MAINTAINERS: Update entries for notification subsystem

Entries for inotify, dnotify, and fanotify in MAINTAINERS are stale.
Neither Eric nor Robert nor John care about these subsystems anymore.
These days it is mostly me or Amir who take care of bugs in these
subsystems. So update MAINTAINERS to reflect current state.

CC: Alexander Viro <viro@zeniv.linux.org.uk>
CC: Eric Paris <eparis@redhat.com>
CC: Robert Love <rlove@rlove.org>
CC: John McCutchan <john@johnmccutchan.com>
CC: Amir Goldstein <amir73il@gmail.com>
Acked-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>