Clean up unused Sliceable.copy()

Sliceable.isCopyableSlice() is not set to true for any controller, so this function is not used.

Usage is removed in Change: I81474aed994678c42d73cc59e169573880de1378

Bug: 227722942
Test: robotest & manual
Change-Id: I86e23aa8ad43f60b5017ff0a278e20e3f727706c

tests/unit/src/com/android/settings/testutils/FakeCopyableController.java

@@ -1,43 +0,0 @@
-/*
- * Copyright (C) 2020 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package com.android.settings.testutils;
-
-import android.content.Context;
-
-import com.android.settings.core.BasePreferenceController;
-
-public class FakeCopyableController extends BasePreferenceController {
-
-    public FakeCopyableController(Context context, String preferenceKey) {
-        super(context, preferenceKey);
-    }
-
-    @Override
-    public int getAvailabilityStatus() {
-        return AVAILABLE;
-    }
-
-    @Override
-    public boolean isSliceable() {
-        return true;
-    }
-
-    @Override
-    public boolean isCopyableSlice() {
-        return true;
-    }
-}