Move ZenModesBackend to SettingsLib.

This will allow us to access it from SystemUI.

Bug: 346519570
Test: builds
Flag: EXEMPT trivial refactor
Change-Id: I5bc480bd4eb0cbf8a26989dd11c064e66e5ee70e

res/drawable/ic_do_not_disturb_on_24dp.xml

@@ -1,28 +0,0 @@
-<!--
-    Copyright (C) 2018 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.
--->
-<vector xmlns:android="http://schemas.android.com/apk/res/android"
-        android:width="24dp"
-        android:height="24dp"
-        android:viewportWidth="24.0"
-        android:viewportHeight="24.0"
-        android:tint="?android:attr/colorControlNormal">
-    <path
-        android:fillColor="#FFFFFFFF"
-        android:pathData="M12,2C6.48,2 2,6.48 2,12c0,5.52 4.48,10 10,10c5.52,0 10,-4.48 10,-10C22,6.48 17.52,2 12,2zM12,20c-4.41,0 -8,-3.59 -8,-8c0,-4.41 3.59,-8 8,-8c4.41,0 8,3.59 8,8C20,16.41 16.41,20 12,20z"/>
-    <path
-        android:fillColor="#FFFFFFFF"
-        android:pathData="M7,11h10v2h-10z"/>
-</vector>