Revert "MessageCache invalidation improvements" (temporary)

Revert "MessageCache invalidation improvements" (temporary)

This reverts commit 9339a08b72c918d7743a9cb286161adb9399a77b
(Change-Id: Idc337a787171949c4f70186b13d7b65304c9b57f).

This is a temporary revert to prevent the change's inclusion in
wmf/1.29.0-wmf.4. That branch is scheduled to be deployed to WMF wikis
during the first week of the WMF's 2016 year-end fundraiser. Since
CentralNotice relies on MessageCache to fetch fundraising banners,
it is preferable not to deploy changes of any significant complexity in
that system at this time.

The original change should be re-applied at a later date. Sincere
apologies to the change's authors! :)

Change-Id: I8330838bbe03ce6ed38fa2e755b44519211d9d43