Tests: Use global no_throttling_everywhere fixture (#701)

Instead of needing to individually disable throttling on a per-plugin
basis, this fixture takes care of all notifiers in `NOTIFY_MODULE_MAP`
automatically. With `autouse=True`, there is no need to activate it
manually.

test/test_plugin_mqtt.py

@@ -57,7 +57,7 @@ def test_plugin_mqtt_paho_import_error(mock_post):
 @pytest.mark.skipif(
     'paho' not in sys.modules, reason="Requires paho-mqtt")
 @mock.patch('paho.mqtt.client.Client')
-def test_plugin_mqtt_general(mock_client, no_throttling):
+def test_plugin_mqtt_general(mock_client):
     """
     NotifyMQTT() General Checks