Eliminate PMs to non-subscribers when creating streams.

This should make stream creation relatively fast again, since we
will no longer send O(N) PMs out to tell folks the stream was
created.

zerver/tests/test_subs.py

@@ -1364,7 +1364,6 @@ class SubscriptionAPITest(ZulipTestCase):
         Calling POST /json/users/me/subscriptions should notify when a new stream is created.
         """
         invitee = "iago@zulip.com"
-        invitee_full_name = 'Iago'
 
         current_stream = self.get_streams(invitee)[0]
         invite_streams = self.make_random_stream_names([current_stream])[:1]
@@ -1378,13 +1377,6 @@ class SubscriptionAPITest(ZulipTestCase):
         )
         self.assert_json_success(result)
 
-        msg = self.get_second_to_last_message()
-        self.assertEqual(msg.recipient.type, Recipient.PERSONAL)
-        self.assertEqual(msg.sender_id, self.notification_bot().id)
-
-        expected_msg = "Hi there!  %s just created a new stream #**%s**." % (invitee_full_name, invite_streams[0])
-        self.assertEqual(msg.content, expected_msg)
-
     def test_successful_subscriptions_notifies_stream(self):
         # type: () -> None
         """

zerver/views/streams.py

@@ -330,26 +330,6 @@ def add_subscriptions_backend(request, user_profile,
                     topic=topic,
                     content=msg))
 
-        else:
-            msg = ("Hi there!  %s just created a new stream #**%s**."
-                   % (user_profile.full_name, created_streams[0].name))
-
-            sender = get_user_profile_by_email(settings.NOTIFICATION_BOT)
-            for realm_user_dict in get_active_user_dicts_in_realm(user_profile.realm):
-                # Don't announce to yourself or to people you explicitly added
-                # (who will get the notification above instead).
-                if realm_user_dict['email'] in principals or realm_user_dict['email'] == user_profile.email:
-                    continue
-
-                recipient_email = realm_user_dict['email']
-
-                notifications.append(
-                    internal_prep_private_message(
-                        realm=user_profile.realm,
-                        sender=sender,
-                        recipient_email=recipient_email,
-                        content=msg))
-
     if not user_profile.realm.is_zephyr_mirror_realm:
         for stream in created_streams:
             notifications.append(prep_stream_welcome_message(stream))