Updated mediawiki/extensions
Project: mediawiki/extensions/Collection  b01562d3ed6df6f1c42fb525c5a8c95e8f4a7cfd

Remove out-of-date README.txt.

The README.rst has the latest/most complete information.  Keeping
multiple copies of the same document in different formats is a bad
idea.

Change-Id: I093b030aaef549357ef124d0621baa468c9b62c5