Change state_information to return feature values (#804)

This changes `state_information` to return the names and values of
all defined features.
It was originally a "temporary" hack to show some extra, device-specific
information in the cli tool, but now that we have device-defined
features we can leverage them.

kasa/iot/iotdimmer.py

@@ -232,12 +232,3 @@ class IotDimmer(IotPlug):
         """Whether the switch supports brightness changes."""
         sys_info = self.sys_info
         return "brightness" in sys_info
-
-    @property  # type: ignore
-    @requires_update
-    def state_information(self) -> Dict[str, Any]:
-        """Return switch-specific state information."""
-        info = super().state_information
-        info["Brightness"] = self.brightness
-
-        return info