[web] update add friends modal selection logic

Summary:
With the new add users modal we now use checkbox ui/ux to select users. This means we can remove the user tags logic we had previously. This diff updates the selection logic and deprecates any unused logic to select a user.

Linear task: https://linear.app/comm/issue/ENG-5957/update-the-ui-of-add-friends-modal

Depends on D10722

Test Plan:
Please see the demo video below

Reviewers: atul, inka

Reviewed By: atul

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10735