[Chromecast] Removed dummy source and manifest.

These are vestiges of gyp and can be removed.

Bug: None
Test: Build cast_shell_apk
Change-Id: I7cdbfe5f7b664def8103354b32be9ce502919bbc
Reviewed-on: https://chromium-review.googlesource.com/1048027Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Simeon Anfinrud <sanfin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556826}

chromecast/android/AndroidManifest.xml

-<?xml version="1.0" encoding="utf-8"?>
-<!--
-  Copyright 2015 The Chromium Authors. All rights reserved.  Use of this
-  source code is governed by a BSD-style license that can be found in the
-  LICENSE file.
--->
-
-<!--
-  This is a dummy manifest which is required by lint for determining min/target
-  SDK version.
--->
-<manifest xmlns:android="http://schemas.android.com/apk/res/android"
-    package="dummy.package">
-
-    <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="22" />
-
-</manifest>

chromecast/android/src/dummy

-Note(gunsch): This file is for the cast_shell_apk target in chromecast.gyp.
-See the notes above that target's 'java_in_dir' variable in chromecast.gyp.