Remove deprecated features from MQTT platforms (#32909)

* Remove deprecated features

* Lint

tests/components/mqtt/test_light_json.py

@@ -91,8 +91,7 @@ import json
 from unittest import mock
 from unittest.mock import patch
 
-from homeassistant.components import light, mqtt
-from homeassistant.components.mqtt.discovery import async_start
+from homeassistant.components import light
 from homeassistant.const import (
     ATTR_ASSUMED_STATE,
     ATTR_SUPPORTED_FEATURES,
@@ -122,7 +121,7 @@ from .common import (
     help_test_update_with_json_attrs_not_dict,
 )
 
-from tests.common import MockConfigEntry, async_fire_mqtt_message, mock_coro
+from tests.common import async_fire_mqtt_message, mock_coro
 from tests.components.light import common
 
 DEFAULT_CONFIG = {
@@ -1061,22 +1060,6 @@ async def test_discovery_removal(hass, mqtt_mock, caplog):
     await help_test_discovery_removal(hass, mqtt_mock, caplog, light.DOMAIN, data)
 
 
-async def test_discovery_deprecated(hass, mqtt_mock, caplog):
-    """Test discovery of mqtt_json light with deprecated platform option."""
-    entry = MockConfigEntry(domain=mqtt.DOMAIN)
-    await async_start(hass, "homeassistant", {"mqtt": {}}, entry)
-    data = (
-        '{ "name": "Beer",'
-        '  "platform": "mqtt_json",'
-        '  "command_topic": "test_topic"}'
-    )
-    async_fire_mqtt_message(hass, "homeassistant/light/bla/config", data)
-    await hass.async_block_till_done()
-    state = hass.states.get("light.beer")
-    assert state is not None
-    assert state.name == "Beer"
-
-
 async def test_discovery_update_light(hass, mqtt_mock, caplog):
     """Test update of discovered light."""
     data1 = (