gfs2: Remove and replace gfs2_glock_queue_work

There are no more callers of gfs2_glock_queue_work() left, so remove
that helper.  With that, we can now rename __gfs2_glock_queue_work()
back to gfs2_glock_queue_work() to get rid of some unnecessary clutter.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>