Remove WBC_VERSION check and namespace from populateInterwiki.php

This script has been the among the most useful thing in all of wikibase!
It has no reason at all to actually require Wikibase and should ideally
be moved into core.

This is one step towards moving this to core.

Change-Id: Iae2fa32fdbb6ebd743d0ae0538942556255ecbd6
Merge "Remove WBC_VERSION check and namespace from populateInterwiki.php"