Make clear_stale_channel_claim implement sticky contact behavior as well
Make clear_stale_channel_claim implement sticky contact behavior as well

Previously, release_channel_for_session would leave the contact in
in the running session info (even while setting the session_id to None)
so that incoming texts would be preferentially treated as coming from
the last active contact; but clear_stale_channel_claim would delete both.

Now, clear_stale_channel_claim adopts this same sticky-contact behavior
as well.

dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq