Removed READ_LATEST from revision load in getMsgFromNamespace()

• The key salting of the invidial keys via the WAN cache makes it OK to use slaves here. The salting happens via the delete() in the MessageCache::replace() call, which is hit when the message page is edited.

Bug: T92357
Change-Id: Ic191f6c3fc49c4c58461d26468dd0fa94a52051e