MXS-1744 Use gtid querying instead of MASTER_GTID_WAIT when waiting for catchup

MASTER_GTID_WAIT uses gtid_slave_pos when comparing to the target gtid. This creates
problems with multi-domain gtids. It's simpler to just query the server for its
gtids repeatedly. Also, the method is now in MariaDBServer.

server/modules/monitor/mariadbmon/gtid.cc

@@ -217,11 +217,6 @@ string Gtid::to_string() const
     return rval;
 }
 
-string GtidList::generate_master_gtid_wait_cmd(double timeout) const
-{
-    return "SELECT MASTER_GTID_WAIT(\"" + to_string() + "\", " + std::to_string(timeout) + ");";
-}
-
 Gtid GtidList::get_gtid(uint32_t domain) const
 {
     Gtid rval;