Do not prompt for password when deleting thread on web

Summary: This differential removes requirement to provide password when deleting thread on web.

Test Plan:
Make hardcoded changes in thread-settings-modal in web so that user can see UI to delete thread. Try deleting thread. "Permission not granted" alert should pop. Now change the code on the keyserver side in thread-deleters not to look at permissions in MySQL. Try deleting again. It should
work.

Reviewers: tomek, atul, ashoat

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D6105