- remove "have_lock" argument from ndb_schema_object functions
 - remove lock of "ndbcluster_mutex" before getting the ndb_schema_object, that is handled in the ndb_schema_object functions
 - no need to check if ndb_schema_object is NULL before releasing it, code would have crashed loong before if it was.
 - add call to release the ndb_schema_object in the CLEAR_SLOCK handler