[keyserver] validate policies only for logged in users

Summary:
Fix for ENG-4978.

An alternative solution is running policiesReducer only when user is logged in to avoid setting flag in store, but changing this on keyserver seems more appropriate, as keyserver should've never throw policies_not_accepted for anonymous user.

Test Plan:
Make sue policies work:

• tested for live session
• tested for logged in

Reviewers: tomek, michal

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D9295