While this is not documented in the spec (but should be), Riot (and other clients) revoke 3PID invites by sending a m.room.third_party_invite event with an empty ({}) content to the room's state.
When the invited 3PID gets associated with a MXID, the identity server (which doesn't know about revocations) sends down to the MXID's homeserver all of the undelivered invites it has for this 3PID. The homeserver then tries to talk to the inviting homeserver in order to exchange these invite for m.room.member events.
When one of the invite is revoked, the inviting homeserver responds with a 500 error because it tries to extract a 'display_name' property from the content, which is empty. This might cause the invited server to consider that the server is down and not try to exchange other, valid invites (or at least delay it).

This fix handles the case of revoked invites by avoiding trying to fetch a 'display_name' from the original invite's content, and letting the m.room.member event fail the auth rules (because, since the original invite's content is empty, it doesn't have public keys), which results in sending a 403 with the correct error message to the invited server.

Fixes #6134.

These tables are unused since #5893 (as amended by #6047), so we can now drop
them.

Fixes #6048.

Reject pending invites on deactivation

Co-Authored-By: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

Co-Authored-By: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

Co-Authored-By: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

Just to have all the methods that make calls to identity services in one place.

Add some helpful opentracing tags and remove get_user_by_req span

Fix 'redaction_retention_period' sampel config to match guidelines

Doing a password reset via SMS has never worked, and in any case is a silly
idea because msisdn recycling is a thing.

See also matrix-org/matrix-doc#2303.

formatting tweak