Fix tank and environment input object cleanup in mock mode

Set the deviceInstance property value directly, instead of calling
_deviceInstance.setValue(), so that BaseDevice::setDeviceInstance() is
called and BaseDevice::validChanged is emitted when the device
instance is set to -1. This ensures the clean up handlers in Tank.qml
and EnvironmentInput.qml are triggered.

Also clean up Tank.qml to use a single signal handler to check whether
the tank needs to be added/removed to/from the tank models.

data/common/Tank.qml

@@ -44,12 +44,10 @@ Device {
 		Component.onCompleted: Qt.callLater(tank._updateMeasurements)
 	}
 
-	onValidChanged: Qt.callLater(tank._updateModel)
-	onTypeChanged: Qt.callLater(tank._updateModel)
-
-	function _updateModel() {
-		if (valid && type >= 0) {
-			if (_tankModel && _tankModel.type !== type) {
+	readonly property bool _deviceAndTypeValid: valid && type >= 0
+	on_DeviceAndTypeValidChanged: {
+		if (_deviceAndTypeValid) {
+			if (_tankModel) {
 				_tankModel.removeDevice(tank.serviceUid)
 			}
 			_tankModel = Global.tanks.tankModel(type)

data/mock/EnvironmentInputsImpl.qml

@@ -85,7 +85,7 @@ Item {
 			const hasCreatedObjects = _createdObjects.length > 0
 			while (_createdObjects.length > 1) {
 				let obj = _createdObjects.pop()
-				obj._deviceInstance.setValue(-1)
+				obj.deviceInstance = -1
 				obj.destroy()
 			}
 
@@ -97,7 +97,7 @@ Item {
 
 			if (hasCreatedObjects) {
 				let lastObject = _createdObjects.shift()
-				lastObject._deviceInstance.setValue(-1)
+				lastObject.deviceInstance = -1
 				lastObject.destroy()
 			}
 		}

data/mock/TanksImpl.qml

@@ -91,7 +91,7 @@ QtObject {
 			const hasCreatedObjects = _createdObjects.length > 0
 			while (_createdObjects.length > 1) {
 				let obj = _createdObjects.pop()
-				obj._deviceInstance.setValue(-1)
+				obj.deviceInstance = -1
 				obj.destroy()
 			}
 
@@ -103,7 +103,7 @@ QtObject {
 
 			if (hasCreatedObjects) {
 				let lastObject = _createdObjects.shift()
-				lastObject._deviceInstance.setValue(-1)
+				lastObject.deviceInstance = -1
 				lastObject.destroy()
 			}
 		}
@@ -132,7 +132,7 @@ QtObject {
 			} else {
 				// remove a tank
 				const index = Math.floor(Math.random() * _createdObjects.length)
-				_createdObjects[index]._deviceInstance.setValue(-1) // causes tank to remove itself from model
+				_createdObjects[index].deviceInstance = -1 // causes tank to remove itself from model
 				_createdObjects.splice(index, 1)
 			}
 		}
@@ -155,7 +155,7 @@ QtObject {
 			root.addTank(tankProperties)
 		} else {
 			for (var i = 0; i < _createdObjects.length; ++i) {
-				_createdObjects[i]._deviceInstance.setValue(-1) // causes tank to remove itself from model
+				_createdObjects[i].deviceInstance = -1 // causes tank to remove itself from model
 			}
 
 			_createdObjects = []