[lib] Update ChangeSettingsMessageSpec robotext for avatar update

Summary:
We don't want to display anything about the updated value since we have no good way to display it (plus the user can just look at the thread header to see the updated avatar).

Depends on D7333

Test Plan:
Before:

After:

Reviewers: ashoat, ginsu

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D7334