dm thin metadata: remove create parameter from __create_persistent_data_objects

Remove 'create' parameter from __create_persistent_data_objects() in dm-thin-metadata.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>