Removed some dead Face Unlock code.

I checked to see if any dead Face Unlock code remains in settings.  Most of it
has been removed, but I did find some strings and an xml file that can be
removed.

Bug: 16139545
Change-Id: I16d7b3a258c72d6788348d1fbe35a7f6bc12ee8e

res/layout/weak_biometric_fallback_header.xml

@@ -1,23 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!-- Copyright (C) 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.
--->
-<TextView xmlns:android="http://schemas.android.com/apk/res/android"
-        android:layout_width="match_parent"
-        android:layout_height="wrap_content"
-        android:padding="8dip"
-        android:gravity="center"
-        android:textAppearance="?android:attr/textAppearanceMedium"
-        android:text="@string/unlock_backup_info_summary"
-/>