Remove extra current_state_events join from queries to grab profile info

[MadLittleMods]

Remove extra current_state_events join from queries to grab profile info

Spawning from #15731

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[MadLittleMods]

I think this is equivalent to the old thing. Please double-check.

I assume room_memberships holds current memberships just as much current_state_events would.

room_memberships is an append-only table which means it holds all membership forever but we only look at Membership.JOIN here which should represent current state since they would be LEAVE or some other membership otherwise.

[MadLittleMods]

The problem with this is that there are multiple entries for a given user_id and we don't know which is the latest just from the room_memberships table alone

Example:

SELECT user_id, display_name, avatar_url FROM room_memberships
WHERE room_id = '!abc:matrix.org' AND membership = 'join';
           user_id            |         display_name          |                avatar_url
------------------------------+-------------------------------+-------------------------------------------
 @madlittlemods:matrix.org    | madlittlemods                 |
 @madlittlemods:matrix.org    | madlittlemods                 | mxc://matrix.org/bDayqThxTIcGNcskzIADknRv
 @madlittlemods:matrix.org    | madlittlemods (Eric Eastwood) | mxc://matrix.org/bDayqThxTIcGNcskzIADknRv