[Predictive Back] Remove OnBackPressedHandler

OnBackPressedHandler was mimicking android.window.OnBackAnimationCallback because later one was hidden API to T.

Now that we have moved to U, we can remove the former handler.

Test: manual
Bug: 272797556
Change-Id: Ic5302cfa0a6fb15c4a64bdf5dc331834b1f06f38
diff --git a/src/com/android/launcher3/AbstractFloatingView.java b/src/com/android/launcher3/AbstractFloatingView.java
index 796fa80..cd9e598 100644
--- a/src/com/android/launcher3/AbstractFloatingView.java
+++ b/src/com/android/launcher3/AbstractFloatingView.java
@@ -24,7 +24,9 @@
 import static com.android.launcher3.compat.AccessibilityManagerCompat.sendCustomAccessibilityEvent;
 
 import android.annotation.SuppressLint;
+import android.annotation.TargetApi;
 import android.content.Context;
+import android.os.Build;
 import android.util.AttributeSet;
 import android.util.Pair;
 import android.view.MotionEvent;
@@ -32,6 +34,7 @@
 import android.view.accessibility.AccessibilityNodeInfo;
 import android.view.animation.Interpolator;
 import android.widget.LinearLayout;
+import android.window.OnBackAnimationCallback;
 
 import androidx.annotation.IntDef;
 
@@ -46,8 +49,9 @@
 /**
  * Base class for a View which shows a floating UI on top of the launcher UI.
  */
+@TargetApi(Build.VERSION_CODES.UPSIDE_DOWN_CAKE)
 public abstract class AbstractFloatingView extends LinearLayout implements TouchController,
-        OnBackPressedHandler {
+        OnBackAnimationCallback {
 
     @IntDef(flag = true, value = {
             TYPE_FOLDER,