fix(preview): remove prepareReadyEvent handler correctly on preview

`tns preview` (and using SK) should remove its handler for prepareControllers' `prepareReadyEvent` handler. However, this does not happend due to two reasons:
- we try to remove the handler from prepareControllers' event, but this handler is attached to `preparController`, so it actually remains and causes multiple issues in long living processes, when CLI is used as a library
- the event handler is not cached correctly as we attach its bound version, but cache it without the binding. So you cannot remove it.

This causes issues when using preview in Sidekick, closing the current app, open it again and try to livesync a change - we have many handlers for prepareReadyEvent and this causes multiple livesync operations.

Author: rosen-vladimirov

lib/controllers/preview-app-controller.ts

@@ -43,7 +43,7 @@ export class PreviewAppController extends EventEmitter implements IPreviewAppCon
 		this.$previewSdkService.stop();
 		this.$previewDevicesService.updateConnectedDevices([]);
 		if (this.prepareReadyEventHandler) {
-			this.removeListener(PREPARE_READY_EVENT_NAME, this.prepareReadyEventHandler);
+			this.$prepareController.removeListener(PREPARE_READY_EVENT_NAME, this.prepareReadyEventHandler);
 			this.prepareReadyEventHandler = null;
 		}
 	}
@@ -83,10 +83,12 @@ export class PreviewAppController extends EventEmitter implements IPreviewAppCon
 				await this.$previewAppPluginsService.comparePluginsOnDevice(data, device);
 
 				if (!this.prepareReadyEventHandler) {
-					this.prepareReadyEventHandler = async (currentPrepareData: IFilesChangeEventData) => {
+					const handler = async (currentPrepareData: IFilesChangeEventData) => {
 						await this.handlePrepareReadyEvent(data, currentPrepareData);
 					};
-					this.$prepareController.on(PREPARE_READY_EVENT_NAME, this.prepareReadyEventHandler.bind(this));
+
+					this.prepareReadyEventHandler = handler.bind(this);
+					this.$prepareController.on(PREPARE_READY_EVENT_NAME, this.prepareReadyEventHandler);
 				}
 
 				data.env = data.env || {};