Remove the ad-hoc cooling override now that COOL handles it natively

TempControllerBase.cooling/set_cooling() forced y=0 in advance of a
Sud ramp-down step; redundant now that the FSM's own COOL state
detects and handles a negative diff itself. Removed from the
controller, SudTask's anticipatory detection (and the Step message's
now-unused "Cooling" field), and demo_sud.py's mirror of it.

gui: the "Cool down" status-bar indicator now reflects the
controller's actual State ("States.COOL") via the TempCtrl channel,
rather than Sud's removed anticipatory flag - renamed
sud_cooling/set_sud_cooling to tc_cooling/set_tc_cooling to match.

client/brewpi_gui.py

@@ -308,10 +308,11 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 		self.statusBar().addPermanentWidget(self.status_label_env)
 		self.update_status_env_label()
 
-		# Blinking indicator for a Sud ramp step that's cooling down
-		# (target below the current temperature - the heater is forced off
-		# server-side and we just wait for ambient loss to catch up).
-		self.sud_cooling = False
+		# Blinking indicator for the temperature controller's own COOL
+		# state (target below the current temperature - the heater is
+		# forced off server-side and we just wait for ambient loss to
+		# catch up).
+		self.tc_cooling = False
 		self.status_label_cooling = QtWidgets.QLabel("Cool down")
 		self.status_label_cooling.setStyleSheet("color: blue; font-weight: bold;")
 		self.status_label_cooling.setVisible(False)
@@ -496,7 +497,7 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 			self.sud_step_type = None
 			self.sud_hold_remaining = 0.0
 			self.forecast_history = []
-			self.set_sud_cooling(False)
+			self.set_tc_cooling(False)
 			self.update_sud_actions()
 			self.update_status_env_label()
 			self.setWindowTitle("BrewPi")
@@ -551,10 +552,10 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 			title += " - {}".format(description)
 		return title
 
-	def set_sud_cooling(self, cooling):
-		if cooling == self.sud_cooling:
+	def set_tc_cooling(self, cooling):
+		if cooling == self.tc_cooling:
 			return
-		self.sud_cooling = cooling
+		self.tc_cooling = cooling
 		if cooling:
 			self.status_label_cooling.setVisible(True)
 			self.cooling_blink_timer.start(500)
@@ -651,6 +652,7 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 		for key in msg:
 			if 'State' in key:
 				self.label_state.setText(msg['State'])
+				self.set_tc_cooling(msg['State'] == 'States.COOL')
 			elif "Soll" in key:
 				submsg = msg['Soll']
 				if 'Temp' in submsg:
@@ -800,7 +802,6 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 				self.sud_step_index = step.get('Index')
 				self.sud_step_descr = step.get('Descr')
 				self.sud_step_type = step.get('Type')
-				self.set_sud_cooling(step.get('Cooling', False))
 				self.update_status_step_label()
 			elif "HoldRemaining" in key:
 				self.sud_hold_remaining = msg['HoldRemaining']