Remove obsolete logic in SettingsActivity.

mIsShowingDashboard is always false, it used to be true when we are
displaying homepage, but now homepage is hosted in a entirely different
activity.

so all related logic can now be removed.

Test: robotests

Misc clean up: remove unused colors

Test: rebuild, color-lint
Change-Id: I1e1628c1e9606c2b7dc40ef3c21d4ed1391a8c03

res/layout/settings_main_dashboard.xml

@@ -1,33 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!--
-/*
-** Copyright 2014, 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.
-*/
--->
-
-<LinearLayout
-    xmlns:android="http://schemas.android.com/apk/res/android"
-    xmlns:app="http://schemas.android.com/apk/res-auto"
-    android:layout_width="match_parent"
-    android:layout_height="match_parent"
-    android:orientation="vertical">
-
-    <include layout="@layout/search_bar" />
-
-    <FrameLayout
-        android:id="@+id/main_content"
-        android:layout_height="match_parent"
-        android:layout_width="match_parent" />
-</LinearLayout>