Remove useless "confirmed" permission assignments

Right at the bottom of CommonSettings.php, there is this bit of code:

// Confirmed can do anything autoconfirmed can.
$wgGroupPermissions['confirmed'] = $wgGroupPermissions['autoconfirmed'];

meaning that the assignment of rights to "confirmed" in groupOverrides is
pointless. It's best not to have bits of code that look like they might do
something but that actually do nothing.

Change-Id: Iab2d61c93bfff68f90bdaeab15443a356768800f