Currently when fetching state groups from the data store we make two
hits two the database: once for members and once for non-members (unless
request is filtered to one or the other). This adds needless load to the
datbase, so this PR refactors the lookup to make only a single database
hit.
don't filter membership events based on history visibility
as we will already have filtered the messages in the timeline, and state events
are always visible.
and because @erikjohnston said so.
