Fix use of incorrect constant RemoveRoleFromObjectACL.

This could cause failures when DROP OWNED BY attempt to remove default
privileges on sequences.  Back-patching to 9.0.

Shigeru Hanada

src/backend/catalog/aclchk.c

@@ -1299,7 +1299,7 @@ RemoveRoleFromObjectACL(Oid roleid, Oid classid, Oid objid)
 			case DEFACLOBJ_RELATION:
 				iacls.objtype = ACL_OBJECT_RELATION;
 				break;
-			case ACL_OBJECT_SEQUENCE:
+			case DEFACLOBJ_SEQUENCE:
 				iacls.objtype = ACL_OBJECT_SEQUENCE;
 				break;
 			case DEFACLOBJ_FUNCTION: