res/res_pjsip_location: Delete contact_status object when contact is deleted

In 450579e9, a change was made that removed the deletion of the
'contact_status' object when a 'contact' object is deleted in sorcery.
This unfortunately means that the 'contact_status' object persists, even when
something has explicitly removed a contact. The result is that the state of
the contact will not be regenerated if that contact is re-created, and the
stale state will be reported/used for that contact. It also results in
no ContactStatusChanged events being generated for either ARI or AMI.

This patch restores the deletion logic that was removed. Doing so now
results in the expected events being generated again.

Change-Id: I28789a112e845072308b5b34522690e3faf58f07