[lib] Add function for filtering out calendar filters related to one keyserver

Summary:
issue: ENG-5810
I added a helper function removeKeyserverThreadIDsFromFilterList, which removes thread ids of theads reladted to given keyservers from calendar filters.
This function is very similar to previously existing removeDeletedThreadIDsFromFilterList, so I extracted the common code

Test Plan: ran the provided tests. The tests for removeDeletedThreadIDsFromFilterList are not very exhaustive, but they check that the functinon didn't stop working as a result of my changes.

Reviewers: michal, kamil, ginsu

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10425