Galera Monitor should not require the REPLICATION CLIENT privilege

The Galera monitor itself does not need the REPLICATION CLIENT privilege, since it has no reason to execute SHOW SLAVE STATUS. Nevertheless, core/monitor.c contains a hardcoded check for this privileged used for all modules.

Granting unnecessary privileges is a security risk, so advice to do so should be avoided.

The permissions required for each monitor should probably be defined by each monitor, not in a central location.