MDEV-23511 shutdown_server 10 times out, causing server kill at shutdown

Shutdown of mtr tests may be too impatient, esp on CI environment where
10 seconds of `arg` of `shutdown_server arg` may not be enough for the clean
shutdown to complete.

This is fixed to remove explicit non-zero timeout argument to
`shutdown_server` from all mtr tests. mysqltest computes 60 seconds default
value for the timeout for the argless `shutdown_server` command.
This policy is additionally ensured with a compile time assert.

mysql-test/suite/multi_source/info_logs.test

@@ -150,7 +150,7 @@ show all slaves status;
 --append_file $MYSQLTEST_VARDIR/tmp/mysqld.3.expect
 restart
 EOF
---shutdown_server 60
+--shutdown_server
 --source include/wait_until_connected_again.inc
 --source include/wait_for_slave_to_start.inc
 set default_master_connection = 'MASTER 2.2';