[lib] Don't display notFriendNotice for the viewer

Summary:
Prior to the changes in D13540, usePotentialMemberItems never got the viewer as an input, so it didn't need to consider it.

It currently sets notFriendNotice for the viewer, which doesn't make sense. While it's true that the viewer is not a friend with themselves, we have no reason to display that notice to the user.

Depends on D13541

Test Plan: Confirm that notFriendNotice no longer appears for the viewer (the viewer's entry in the list of users that can be added to the chat)

Reviewers: tomek, kamil, inka

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D13542