Remove unused drawables

Change-Id: I83f752dcb0d607e3f77bfbee519993aa37bfd5e4

java/res/drawable/btn_center.xml

@@ -1,40 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!--
-/*
-**
-** Copyright 2011, 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.
-*/
--->
-
-<selector
-        xmlns:android="http://schemas.android.com/apk/res/android"
-        android:exitFadeDuration="@android:integer/config_mediumAnimTime">
-    <item
-        android:state_window_focused="false"
-        android:state_enabled="true"
-        android:drawable="@drawable/btn_center_default" />
-    <item
-        android:state_pressed="true"
-        android:drawable="@drawable/btn_center_pressed" />
-    <item
-        android:state_focused="true"
-        android:state_enabled="true"
-        android:drawable="@drawable/btn_center_selected" />
-    <item
-        android:state_enabled="true"
-        android:drawable="@drawable/btn_center_default" />
-    <item
-        android:drawable="@drawable/btn_center_default" />
-</selector>