Changes in SignonAuthSession

The long deprecated signon_auth_session_process() has been removed and the signon_auth_session_process_async() method has been renamed to signon_auth_session_process() as asynchronous methods are the default way to use this API.

signon_auth_session_query_available_mechanisms() has been removed and can be replaced by signon_auth_service_get_mechanisms() with a manual filtering if needed.