Ignore password when deleting thread on the server side

Summary: This differential makes keyserver ignore password coming in thread deletion request.

Test Plan: Create SIWE account, give it relevant privilages (for example hardcode canDeleteThread to be always true). Enter chat settings and delete chat providing any password. Ensure thread is deleted

Reviewers: tomek, atul

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D6102