Revert "Make obsolete site object can be created"

Note to self: actually run *all* tests. Apparently we have a duplicate set of must_be tests >_<

See https://travis-ci.org/wikimedia/pywikibot-core/jobs/21351801

This reverts commit b548a1afb74ba26d1acd508e8b6ed14f03a368ee.

Change-Id: Icd6ddbc18d0515ec4f3f786dd7eb990e064bab8c
Merge "Revert "Make obsolete site object can be created""