[Bouncer] Remove duplicate manage users.

Remove a duplicate manage users menu item in the user switcher activity.

A manage users action was added further upstream for the data sources
with the new impl and old impl, therefore manually
adding the manage users action is not necessary for newimpl or oldimpl.
This was removed before, but there seemed to be a faulty merge conflict
resolution on my part.

Bug: 241811308, 254257455
Test: Observed 2 manage users in the User switchers before my change.
Observed 1 manage users action after my change.

Change-Id: I23efa9fedb6987e6427954662c07229767802bb8