Updated mediawiki/extensions
Project: mediawiki/extensions/MassMessage  24caa7d8cb85e3cb5aa779066ad608b5760adcc2

Clean up SpecialMassMessage

Minor refactor of some logic and clean up some comments. Should not
change actual behaviour.

Change-Id: I7a92825edf24de0ad3c01f5b91b16982e79faa62