MDEV-17544 No warning when trying to name a primary key constraint.

Warning added.

mysql-test/suite/rpl/r/rpl_blackhole_row_annotate.result

@@ -47,6 +47,8 @@ COUNT(*)
 >>> Something was written to binary log <<<
 connection master;
 ALTER TABLE t1 ADD PRIMARY KEY pk_t1 (a,b);
+Warnings:
+Warning	1280	Name 'pk_t1' ignored for PRIMARY key.
 connection slave;
 connection master;
 INSERT INTO t1 VALUES (1,2,1),(2,2,2),(3,2,3),(4,2,4);