[mqtt] Stop sending deprecated color_mode and brightness in light discovery (fixes #13666) (#13667)

esphome/components/mqtt/mqtt_light.cpp

@@ -47,7 +47,6 @@ void MQTTJSONLightComponent::send_discovery(JsonObject root, mqtt::SendDiscovery
   root[ESPHOME_F("schema")] = ESPHOME_F("json");
   auto traits = this->state_->get_traits();
 
-  root[MQTT_COLOR_MODE] = true;
   // NOLINTNEXTLINE(clang-analyzer-cplusplus.NewDeleteLeaks) false positive with ArduinoJson
   JsonArray color_modes = root[ESPHOME_F("supported_color_modes")].to<JsonArray>();
   if (traits.supports_color_mode(ColorMode::ON_OFF))
@@ -68,10 +67,6 @@ void MQTTJSONLightComponent::send_discovery(JsonObject root, mqtt::SendDiscovery
   if (traits.supports_color_mode(ColorMode::RGB_COLD_WARM_WHITE))
     color_modes.add(ESPHOME_F("rgbww"));
 
-  // legacy API
-  if (traits.supports_color_capability(ColorCapability::BRIGHTNESS))
-    root[ESPHOME_F("brightness")] = true;
-
   if (traits.supports_color_mode(ColorMode::COLOR_TEMPERATURE) ||
       traits.supports_color_mode(ColorMode::COLD_WARM_WHITE)) {
     root[MQTT_MIN_MIREDS] = traits.get_min_mireds();