MDEV-22472 rpl.rpl_fail_register failed in buildbot with wrong result

This is a new test from upstream that did not expect the correct value
of the command slot of the Dump thread when the latter gets killed.

The test is made to expect "Killed" string as the command
in show-processlist as it is supposed to when a thread gets killed.

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

@@ -17,12 +17,11 @@ set global debug_dbug=@old_dbug;
 
 connection master;
 
-### why is that needed?
 let $id=`SELECT id from information_schema.processlist where command='Binlog Dump'`;
 if ($id) {
   replace_result $id DUMP_THREAD;
   eval kill $id;
-  let $wait_condition= SELECT count(*)=0 from information_schema.processlist where command='Binlog Dump';
+  let $wait_condition= SELECT count(*)=0 from information_schema.processlist where command='Killed';
   source include/wait_condition.inc;
 }