[lib] Enable thick thread creation for all the users

Summary:
Delete a hook that was limiting this options to the staff users.

https://linear.app/comm/issue/ENG-9360/enable-thick-threads-for-all-the-users

Test Plan: Flow. A sanity check about creating and leaving a thread.

Reviewers: kamil, will, inka

Reviewed By: kamil, inka

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D13423