When I was talking to Matthew about this the other day, we couldn't think of a
good reason why we should preserve the HS URL at logout. It introduces the
problem that, if a client is redirected after login as per MSC1730, and then
you log out, you'll then get a login screen for the wrong server.
So basically there's no reason to have an mx_hs_url/mx_is_url without an access
token, and we can remove the stuff which preserves it, and the stuff that
attempts to restore it.
Richard van der Hoff
36dd43f734