Remove ReactViewGroup.getBackgroundColor() (#47906)

Summary:
Pull Request resolved: #47906

There are no usages in the repo.  External usages should be using [BackgroundStyleApplicator](https://github.com/facebook/react-native/blob/main/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/BackgroundStyleApplicator.kt#L82).

Changelog: [Android][Breaking] Removed ReactViewGroup.getBackgroundColor()

Reviewed By: NickGerleman

Differential Revision: D66368623

fbshipit-source-id: bf173efc7e40d3d8a5d55ba0f82eed49b4cb2746

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/view/ReactViewGroup.java

@@ -15,7 +15,6 @@
 import android.content.Context;
 import android.graphics.BlendMode;
 import android.graphics.Canvas;
-import android.graphics.Color;
 import android.graphics.Paint;
 import android.graphics.Rect;
 import android.graphics.drawable.Drawable;
@@ -33,7 +32,6 @@
 import com.facebook.react.bridge.ReactNoCrashSoftException;
 import com.facebook.react.bridge.ReactSoftExceptionLogger;
 import com.facebook.react.bridge.UiThreadUtil;
-import com.facebook.react.common.annotations.VisibleForTesting;
 import com.facebook.react.config.ReactFeatureFlags;
 import com.facebook.react.touch.OnInterceptTouchEventListener;
 import com.facebook.react.touch.ReactHitSlopView;
@@ -72,7 +70,6 @@ public class ReactViewGroup extends ViewGroup
         ReactOverflowViewWithInset {
 
   private static final int ARRAY_CAPACITY_INCREMENT = 12;
-  private static final int DEFAULT_BACKGROUND_COLOR = Color.TRANSPARENT;
   private static final LayoutParams sDefaultLayoutParam = new ViewGroup.LayoutParams(0, 0);
   private final Rect mOverflowInset = new Rect();
 
@@ -760,12 +757,6 @@ private boolean needsIsolatedLayer() {
     return false;
   }
 
-  @VisibleForTesting
-  public int getBackgroundColor() {
-    @Nullable Integer color = BackgroundStyleApplicator.getBackgroundColor(this);
-    return color == null ? DEFAULT_BACKGROUND_COLOR : color;
-  }
-
   @Override
   public @Nullable Rect getHitSlopRect() {
     return mHitSlopRect;