ctdb_ltdb_store_server: delete an empty record that is safe to delete instead of...

ctdb_ltdb_store_server: delete an empty record that is safe to delete instead of storing locally.

When storing a record that is being migrated off to another node
and has never been migrated with data, then we can safely delete it
from the local tdb instead of storing the record with empty data.

Note: This record is not deleted if we are its lmaster or dmaster.

Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>
(cherry picked from commit 3cca0d4b48325d86de2cb0b44bb7811a30701352)

Signed-off-by: Stefan Metzmacher <metze@samba.org>