Make Promise::resolve_native actually sound

We shouldn't have to pass a raw JSContext pointer, and to enter the
promise's context's compartment by hand.

components/script/dom/bluetoothdevice.rs

@@ -273,7 +273,7 @@ impl AsyncBluetoothListener for BluetoothDevice {
                 // Step 3.1.
                 self.watching_advertisements.set(true);
                 // Step 3.2.
-                promise.resolve_native(promise_cx, &());
+                promise.resolve_native(&());
             },
             _ => promise.reject_error(promise_cx, Error::Type("Something went wrong...".to_owned())),
         }