LU-10467 lov: use wait_event() in lov_subobject_kill()

LU-10467 lov: use wait_event() in lov_subobject_kill()

lov_subobject_kill() has an open-coded version
of wait_event(). Change it to use the macro.

There is no need to take a spinlock just to check if a variable
have changed value. If there was, the first test would be protected too.

"lti_waiter" now has no users and can be removed from lov_thread_info.

Change-Id: Ic1126fc500c03c48c4426171e98590ef6dce3098
Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-on: https://review.whamcloud.com/36343
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>