Remove require mysql::db from gerrit init

We don't use it anymore so it's difficult to require it.

Apr 23 19:20:26 review puppet-agent[3736]: Could not retrieve catalog from remote server: Error 400 on SERVER: Invalid relationship: Exec[gerr
it-initial-init] { require => Mysql::Db[reviewdb] }, because Mysql::Db[reviewdb] doesn't seem to be in the catalog

Change-Id: Id4b69be61351274512e7784594b391e5fab2a482