Deprecate ApiQueryRevisionContentFlow.

Its functionality is duplicated in the more generic ApiQueryFlow, and both occasions
where it was used were in situations where the data in question was already available
from other sources without an API call.

Also moved ui-functions.js to the base module instead of the discussion module.

Change-Id: I834ab83e532b14c957d629e1a2de161b1180d9ca
Merge "Deprecate ApiQueryRevisionContentFlow."