Remove som GYP annotations, remove unused manifest.

testing/android/native_test/BUILD.gn

Index: testing/android/native_test/BUILD.gn
diff --git a/testing/android/native_test/BUILD.gn b/testing/android/native_test/BUILD.gn
index 3f2868bc250cbd4f4c43eb613174645beacb3069..971c423305da06ba2e11f741699c7117076f8695 100644
--- a/testing/android/native_test/BUILD.gn
+++ b/testing/android/native_test/BUILD.gn
@@ -4,7 +4,6 @@
 
 import("//build/config/android/rules.gni")
 
-# GYP: //testing/android/native_test.gyp:native_test_support
 source_set("native_test_support") {
   testonly = true
   sources = [
@@ -22,7 +21,6 @@ source_set("native_test_support") {
   ]
 }
 
-# GYP: //testing/android/native_test.gyp:native_test_native_code
 source_set("native_test_native_code") {
   testonly = true
   sources = [
@@ -35,7 +33,6 @@ source_set("native_test_native_code") {
   ]
 }
 
-# GYP: //testing/android/native_test.gyp:native_test_java
 android_library("native_test_java") {
   testonly = true
   deps = [
@@ -56,7 +53,6 @@ android_library("native_test_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",