ha: color_mode flag is deprecated (#2634)

Deprecated flag `color_mode` used in MQTT JSON light config , the `color_mode` flag is not used anymore and should be removed.
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This will stop working in Home Assistant Core 2025.3

code/espurna/homeassistant.cpp

@@ -621,7 +621,6 @@ class LightDiscovery : public Discovery {
             //   'rgbww' - we receive and map 'c' to our 'cold' and 'w' to our 'warm'
             //   'cw' / 'ww' without 'rgb' are not supported; see 'brightness' or 'color_temp'
             json["brightness"] = true;
-            json["color_mode"] = true;
             JsonArray& modes = json.createNestedArray("supported_color_modes");
 
             if (lightHasColor()) {