Don't invoke removeObserver in deinit

According to Apple's documentation, this method invocation should not be needed anymore.
```
If your app targets iOS 9.0 and later or macOS 10.11 and later, you don't need to unregister an observer in its dealloc method.
```

lottie-swift/src/Public/Animation/AnimationView.swift

@@ -618,10 +618,6 @@ final public class AnimationView: LottieView {
  commonInit()
  }
 
- deinit {
- NotificationCenter.default.removeObserver(self)
- }
-
  // MARK: - Public (UIView Overrides)
 
  override public var intrinsicContentSize: CGSize {