Remove som GYP annotations, remove unused manifest.

build/secondary/third_party/android_tools/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/android/rules.gni")
 
 config("cpu_features_include") {
   include_dirs = [ "$android_ndk_root/sources/android/cpufeatures" ]
 }
 
 config("cpu_features_warnings") {
   if (is_clang) {
     # cpu-features.c has few unused functions on x86 b/26403333
     cflags = [ "-Wno-unused-function" ]
   }
 }
 
-# This is the GN version of
-# //build/android/ndk.gyp:cpu_features
 source_set("cpu_features") {
   sources = [
     "$android_ndk_root/sources/android/cpufeatures/cpu-features.c",
   ]
   public_configs = [ ":cpu_features_include" ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [
     "//build/config/compiler:no_chromium_code",
 
@@ skipping 108 matching lines @@
   ]
   lib_name = "leanback-v17"
   aar_path = "$lib_path/$lib_name/$lib_version/$lib_name-$lib_version.aar"
 }
 
 # TODO(jbudorick): Remove this once net_java_test_support no longer needs it.
 android_java_prebuilt("legacy_http_javalib") {
   testonly = true
   jar_path = "$android_sdk/optional/org.apache.http.legacy.jar"
 }