mavlink: replace MavlinkOrbSubscription with uORB::Subscription

* uORB orb_stat() and update(uint64_t *time, void *dst) are now obsolete and have been deleted
 * mavlink messages add more advertised checks in streams get_size() check to improve data rate calculation across different scenarios

Tools/uorb_graph/create.py

@@ -221,7 +221,6 @@ class Graph(object):
     #   to this, so that we can ignore it)
         special_cases_sub = [
     ('sensors', r'voted_sensors_update\.cpp$', r'\binitSensorClass\b\(([^,)]+)', r'^meta$'),
-    ('mavlink', r'.*', r'\badd_orb_subscription\b\(([^,)]+)', r'^_topic$'),
     ('listener', r'.*', None, r'^(id)$'),
     ('logger', r'.*', None, r'^(topic|sub\.metadata|_polling_topic_meta)$'),