Revert^2 "Nullability Annotations replacement"

This reverts commit 19d1d3d15d.

Reason for revert: revert it because this is not the root cause.

bug: 316867690
Change-Id: I0f168dbb64044aa720202af7b1040afd4f028c9c

src/com/android/settings/slices/SliceBackgroundWorker.java

@@ -17,7 +17,6 @@
 package com.android.settings.slices;
 
 import android.annotation.MainThread;
-import android.annotation.Nullable;
 import android.content.Context;
 import android.net.Uri;
 import android.os.Handler;
@@ -29,6 +28,7 @@ import android.os.SystemClock;
 import android.util.ArrayMap;
 import android.util.Log;
 
+import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
 
 import java.io.Closeable;