* Remove m.thread filter from relations API call
We used MSC3981 to pass the recurse param to the /relations
endpoint so that we could get relations to events in a thread, but
we kept the rel_type filter on (as m.thread) so no second-order relations
would ever have been returned (a nested thread isn't a thing).
This removes the filter and does some filtering on the client side to
remove any events that shouldn't live in the threaded timeline (ie.
non-thread relations to the thread root event).
This should help fix stuck unreads because it will avoid the event that
the receipt refers to going missing (but only on HSes that support MSC3981).
For https://github.com/vector-im/element-web/issues/26718
* Fix import cycle
* Remove params from expected calls in tests to match
* Unused import
