Some Client related cleanups

Summary:
Client up `client.device` (which had no code references anymore) / `client.deviceSync`. Cleaned up feature code for old SDKs (pre 2, which is 3 years old).

This makes decapitating Client a little simpler in the rest of the stack.

Reviewed By: passy

Differential Revision: D31235436

fbshipit-source-id: 919679c1830e2b9368d0787d7b363c090305edb8

desktop/app/src/dispatcher/flipperServer.tsx

@@ -173,8 +173,7 @@ export async function handleClientConnected(store: Store, client: Client) {
     payload: client,
   });
 
-  // eslint-disable-next-line node/no-sync
-  const device = client.deviceSync;
+  const device = client.device;
   if (device) {
     store.dispatch(selectDevice(device));
     store.dispatch(selectClient(client.id));