Delete broken demo video

Author: dhfmzk

README.md

@@ -27,10 +27,6 @@ public class BluetoothController : MonoBehaviour, IBtObserver {
 ```
 3. Now, you can refer to the event method list and design it in detail. :)
 
-Demo
-----
-[![Demo video](https://img.youtube.com/vi/mqlsbmmahVs/0.jpg)](https://www.youtube.com/watch?v=mqlsbmmahVs)
-
 License
 -------
 Copyright 2017 The Android Open Source Project, Inc.