res_pjsip_mwi: remove unneeded check on endpoint's contacts.

res_pjsip_mwi: remove unneeded check on endpoint's contacts.

The function create_mwi_subscriptions_for_endpoint checks
if there is active contacts by retrieving aors and contacts.

This function is used to create all unsolicited mwi subscriptions
on startup and is used when contact added.

In both cases it's not necessary to check if there are contacts.
The contacts are needed when asterisk sends mwi.

ASTERISK-26200 #close

Change-Id: I98e43bdc97f3c0829951cd9bf5f3c6348c6ac1fa