(bug 48381) remove obsolete js/css entries from $wgWhitelistRead

There is no longer any reason for non-logged-in users to be able
to access Monobook.css/js or "-", now that the ResourceLoader
infrastructure is in place.

Bug: 48381
Change-Id: I24ada07f1f55644ba5303c1fcd8e3909067c7c7b