dlm: fix removal of rsb struct that is master and dir record

An rsb struct was not being removed in the case where it
was both the master and the dir record.  This case (master
and dir node) was missed in the condition for doing add_scan()
from deactivate_rsb().  Fixing this triggers a related WARN_ON
that needs to be fixed, and requires adjusting where two
del_scan() calls are made.

Fixes: c217adfc ("dlm: fix add_scan and del_scan usage")
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>