Fix sporadic failure of test case rpl.rpl_old_master

Remove the test for MDEV-14528. This is supposed to test that parallel
replication from pre-10.0 master will update Seconds_Behind_Master. But
after MDEV-12179 the SQL thread is blocked from even beginning to fetch
events from the relay log due to FLUSH TABLES WITH READ LOCK, so the test
case is no longer testing what is was intended to. And pre-10.0 versions are
long since out of support, so does not seem worthwhile to try to rewrite the
test to work another way.

The root cause of the test failure is MDEV-34778. Briefly, depending on
exact timing during slave stop, the rli->sql_thread_caught_up flag may end
up with different value. If it ends up as "true", this causes
Seconds_Behind_Master to be 0 during next slave start; and this caused test
case timeout as the test was waiting for Seconds_Behind_Master to become
non-zero.
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>

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

@@ -9,10 +9,7 @@ connection slave;
 SET @old_parallel= @@GLOBAL.slave_parallel_threads;
 SET GLOBAL slave_parallel_threads=10;
 CHANGE MASTER TO master_host='127.0.0.1', master_port=SERVER_MYPORT_1, master_user='root', master_log_file='master-bin.000001', master_log_pos=4;
-FLUSH TABLES WITH READ LOCK;
 include/start_slave.inc
-include/wait_for_slave_param.inc [Seconds_Behind_Master]
-UNLOCK TABLES;
 connection master;
 CREATE TABLE t2 (a INT PRIMARY KEY) ENGINE=InnoDB;
 INSERT INTO t2 VALUES (1);

mysql-test/suite/rpl/t/rpl_old_master.test

@@ -28,14 +28,7 @@ SET GLOBAL slave_parallel_threads=10;
 --replace_result $SERVER_MYPORT_1 SERVER_MYPORT_1
 eval CHANGE MASTER TO master_host='127.0.0.1', master_port=$SERVER_MYPORT_1, master_user='root', master_log_file='master-bin.000001', master_log_pos=4;
 
-# Block execution yet when the blocked query timestamp has been already accounted
-FLUSH TABLES WITH READ LOCK;
 --source include/start_slave.inc
---let $slave_param           = Seconds_Behind_Master
---let $slave_param_value     = 1
---let $slave_param_comparison= >=
---source include/wait_for_slave_param.inc
-UNLOCK TABLES;
 
 --connection master
 CREATE TABLE t2 (a INT PRIMARY KEY) ENGINE=InnoDB;