Revert "Make obsolete site object can be created"

Breaks tests: https://travis-ci.org/wikimedia/pywikibot-core/builds/20728728

This reverts commit 70d384f3b526123909868d86828c31712500edd1.

Change-Id: I9e72cd6cf77065c0264ec6753d6c1ee9db1eec92
Merge "Revert "Make obsolete site object can be created""