Remove server-side Activate/Enable residues from heater and tempctrl tasks

HeaterTask.on_changed_active() was never registered as a callback so
never fired; TcTask.recv() no longer needs to handle {Enable: ...}
since no client sends it after the override checkbox removal.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DF16nV2ispNw1C9SbvqbRQ

tasks/heater.py

@@ -22,9 +22,6 @@ class HeaterTask(ATask):
 	def actor(self, y):
 		self.power_actor = max(0, self.device.get_power_max() * y)
 
-	def on_changed_active(self, is_activated):
-		asyncio.create_task(self.send({'Activate': int(is_activated)}))
-
 	def on_changed_power(self, power):
 		asyncio.create_task(self.send({'Power': power}))