[identity] Remove references to "devices" attr in users table

Summary:
Part of ENG-5842.
This diff removes almost all code that referenced "devices" attribute in users table. The code left is not nice, further refactors are done in subsequent diffs.

The only part left is adding devices to the list, which is done separately in D10698 (I had to reverse diff order to make CI pass)

Test Plan: Identity integration tests

Reviewers: varun, michal

Reviewed By: varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10699