Added AnimatedValueXY.removeAllListeners

Summary:
> Explain the **motivation** for making this change. What existing problem does the pull request solve?

`AnimatedValueX` has `removeAllListeners()` which is a convenient way to do cleanup when components unmount, but `AnimatedValueXY` was missing a similar method which doesn't really make sense. This change makes the two classes more similar, less confusing and more convenient.
Closes #11783

Differential Revision: D4397188

fbshipit-source-id: d10a0c9c7e0a83af015ec04f6facf965d95ea984

Libraries/Animated/src/AnimatedImplementation.js

@@ -1030,6 +1030,12 @@ class AnimatedValueXY extends AnimatedWithChildren {
     delete this._listeners[id];
   }
 
+  removeAllListeners(): void {
+    this.x.removeAllListeners();
+    this.y.removeAllListeners();
+    this._listeners = {};
+  }
+
   /**
    * Converts `{x, y}` into `{left, top}` for use in style, e.g.
    *