Fix MQTT config schema to ensure correct validation (#73619)

* Ensure config schema validation

* Use correct schema for device_tracker

* Remove schema validation from the platform setup

* Remove loop to build schema

homeassistant/components/mqtt/select.py

@@ -95,9 +95,7 @@ async def async_setup_entry(
     """Set up MQTT select through configuration.yaml and dynamically through MQTT discovery."""
     # load and initialize platform config from configuration.yaml
     config_entry.async_on_unload(
-        await async_setup_platform_discovery(
-            hass, select.DOMAIN, PLATFORM_SCHEMA_MODERN
-        )
+        await async_setup_platform_discovery(hass, select.DOMAIN)
     )
     # setup for discovery
     setup = functools.partial(