Remove som GYP annotations, remove unused manifest.

testing/android/native_test/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")
 
-# GYP: //testing/android/native_test.gyp:native_test_support
 source_set("native_test_support") {
   testonly = true
   sources = [
     "native_test_launcher.cc",
     "native_test_launcher.h",
     "native_test_util.cc",
     "native_test_util.h",
   ]
   deps = [
     ":native_test_jni_headers",
     "//base",
     "//base/test:test_support",
     "//base/third_party/dynamic_annotations",
     "//testing/gtest",
   ]
 }
 
-# GYP: //testing/android/native_test.gyp:native_test_native_code
 source_set("native_test_native_code") {
   testonly = true
   sources = [
     "native_test_jni_onload.cc",
   ]
   libs = [ "log" ]
   deps = [
     ":native_test_support",
     "//base",
   ]
 }
 
-# GYP: //testing/android/native_test.gyp:native_test_java
 android_library("native_test_java") {
   testonly = true
   deps = [
     "//base:base_java",
     "//base:base_java_test_support",
     "//testing/android/appurify_support:appurify_support_java",
     "//testing/android/reporter:reporter_java",
   ]
   srcjar_deps = [ "//base:base_native_libraries_gen" ]
   java_files = [
     "java/src/org/chromium/native_test/NativeBrowserTestActivity.java",
     "java/src/org/chromium/native_test/NativeTest.java",
     "java/src/org/chromium/native_test/NativeTestInstrumentationTestRunner.java",
     "java/src/org/chromium/native_test/NativeUnitTest.java",
     "java/src/org/chromium/native_test/NativeUnitTestActivity.java",
     "java/src/org/chromium/native_test/NativeUnitTestNativeActivity.java",
   ]
   jar_excluded_patterns = [ "*/NativeLibraries.class" ]
 }
 
-# GYP: //testing/android/native_test.gyp:native_test_jni_headers
 generate_jni("native_test_jni_headers") {
   sources = [
     "java/src/org/chromium/native_test/NativeTest.java",
   ]
   jni_package = "testing"
 }