Revert "rdbms: add domain sanity checks to LoadBalancer connection methods"

Revert "rdbms: add domain sanity checks to LoadBalancer connection methods"

This reverts commit b416e166a3eba1dcfc2e912e37e443981d7f60ef.

Fails on Travis CI / PHP 7.1 / Postgres:

> Creating administrator user account
>
> UnexpectedValueException:
> Got connection to 'traviswiki-mediawiki', but expected 'traviswiki'.
>
> Backtrace:
> #0 includes/libs/rdbms/loadbalancer/LoadBalancer.php(887): Wikimedia\Rdbms\LoadBalancer->openForeignConnection(integer, string, integer)
> #1 includes/libs/rdbms/loadbalancer/LoadBalancer.php(766): Wikimedia\Rdbms\LoadBalancer->openConnection(integer, string, integer)
> #2 includes/libs/rdbms/loadbalancer/LoadBalancer.php(851): Wikimedia\Rdbms\LoadBalancer->getConnection(integer, array, string, integer)
> #3 includes/jobqueue/JobQueueDB.php(780): Wikimedia\Rdbms\LoadBalancer->getConnectionRef(integer, array, string, integer)
> #4 includes/jobqueue/JobQueueDB.php(761): JobQueueDB->getDB(integer)
> #5 includes/jobqueue/JobQueueDB.php(187): JobQueueDB->getMasterDB()
> #6 includes/jobqueue/JobQueue.php(332): JobQueueDB->doBatchPush(array, integer)
> #7 includes/jobqueue/JobQueue.php(302): JobQueue->batchPush(array, integer)
> #8 includes/jobqueue/JobQueueGroup.php(154): JobQueue->push(array)
> #9 includes/user/UserGroupMembership.php(162): JobQueueGroup->push(array)
> #10 includes/user/User.php(3733): UserGroupMembership->insert(boolean)
> #11 includes/installer/Installer.php(1680): User->addGroup(string)
> #12 includes/installer/Installer.php(1601): Installer->createSysop(PostgresInstaller)
> #13 includes/installer/CliInstaller.php(176): Installer->performInstallation(array, array)

Change-Id: I269df89d47cc5a183af630447cd1642d3d4a3deb