* add some tests to verify we are stripping unauthorized fields out of unsigned

* add function to strip unauthorized fields from the unsigned object of event

* newsfragment

* update newsfragment number

* add check to on_send_membership_event

* refactor tests

* fix lint error

* slightly refactor tests and add some comments

* slight refactor

* refactor tests

* fix import error

* slight refactor

* remove unsigned filtration code from synapse/handlers/federation_event.py

* lint

* move unsigned filtering code to event base

* refactor tests

* update newsfragment

* requested changes

* remove unused retun values