Fix issue server-core not cleaning up devices properly

Summary:
Notice during debugging that devices keep unregistering. Doesn't lead to any practical issues, but still incorrect.

Also noticed that the server didn't restart when changing flipper-server-core, or recompile its deps, so fixed that as well.

Reviewed By: passy

Differential Revision: D32644276

fbshipit-source-id: 5384a30c9d293acda04b6e6f940268ddcd65a870

desktop/flipper-server-core/src/FlipperServerImpl.tsx

@@ -275,6 +275,7 @@ export class FlipperServerImpl implements FlipperServer {
     if (!device) {
       return;
     }
+    this.devices.delete(serial);
     device.disconnect(); // we'll only destroy upon replacement
     this.emit('device-disconnected', device.info);
   }