BREAKING - Remove LayoutAnimation experimental flag on Android

Summary:
I don't remember exactly where we talked about this but LayoutAnimation on Android is pretty stable now so there's no reason to keep it behind an experimental flag anymore. The only part that is not really stable is delete animations, so what I did is remove the default delete animation that we provide in presets.

**Test plan**
Tested that layout animations work properly without any config.
Closes https://github.com/facebook/react-native/pull/12141

Differential Revision: D4494386

Pulled By: mkonicek

fbshipit-source-id: 5dd025584e35f9bff25dc299cc9ca5c5bf5f17a3

ReactAndroid/src/main/java/com/facebook/react/uimanager/UIImplementation.java

@@ -569,21 +569,6 @@ public class UIImplementation {
     mOperationsQueue.enqueueRemoveAnimation(animationID);
   }
 
-  /**
-   * LayoutAnimation API on Android is currently experimental. Therefore, it needs to be enabled
-   * explicitly in order to avoid regression in existing application written for iOS using this API.
-   *
-   * Warning : This method will be removed in future version of React Native, and layout animation
-   * will be enabled by default, so always check for its existence before invoking it.
-   *
-   * TODO(9139831) : remove this method once layout animation is fully stable.
-   *
-   * @param enabled whether layout animation is enabled or not
-   */
-  public void setLayoutAnimationEnabledExperimental(boolean enabled) {
-    mOperationsQueue.enqueueSetLayoutAnimationEnabled(enabled);
-  }
-
   /**
    * Configure an animation to be used for the native layout changes, and native views
    * creation. The animation will only apply during the current batch operations.