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

src/com/android/settings/deviceinfo/PhoneNumberPreferenceController.java

@@ -16,16 +16,11 @@
 
 package com.android.settings.deviceinfo;
 
-import static android.content.Context.CLIPBOARD_SERVICE;
-
-import android.content.ClipData;
-import android.content.ClipboardManager;
 import android.content.Context;
 import android.telephony.SubscriptionInfo;
 import android.telephony.SubscriptionManager;
 import android.telephony.TelephonyManager;
 import android.text.TextUtils;
-import android.widget.Toast;
 
 import androidx.annotation.VisibleForTesting;
 import androidx.preference.Preference;
@@ -98,17 +93,6 @@ public class PhoneNumberPreferenceController extends BasePreferenceController {
         return true;
     }
 
-    @Override
-    public void copy() {
-        final ClipboardManager clipboard = (ClipboardManager) mContext.getSystemService(
-                CLIPBOARD_SERVICE);
-        clipboard.setPrimaryClip(ClipData.newPlainText("text", getFirstPhoneNumber()));
-
-        final String toast = mContext.getString(R.string.copyable_slice_toast,
-                mContext.getText(R.string.status_number));
-        Toast.makeText(mContext, toast, Toast.LENGTH_SHORT).show();
-    }
-
     private CharSequence getFirstPhoneNumber() {
         final List<SubscriptionInfo> subscriptionInfoList =
                 mSubscriptionManager.getActiveSubscriptionInfoList();