Remove assertion that prevents zfs rename of datasets with mountpoint=none

or mountpoint=legacy that have children datasets. This also fixes dataset
rename when receiving incremental snapshots as reported on freebsd-fs@

This assertion was made triggerable by opensolaris change #10196.

PR:		bin/160400
Reviewed by:	pjd
MFC after:	1 week

cddl/contrib/opensolaris/lib/libzfs/common/libzfs_changelist.c

@@ -467,7 +467,6 @@ change_one(zfs_handle_t *zhp, void *data)
 			 * This is necessary when the original mountpoint
 			 * is legacy or none.
 			 */
-			ASSERT(!clp->cl_alldependents);
 			verify(uu_list_insert_before(clp->cl_list,
 			    uu_list_first(clp->cl_list), cn) == 0);
 		}