Remove som GYP annotations, remove unused manifest.

content/public/test/android/BUILD.gn

Index: content/public/test/android/BUILD.gn
diff --git a/content/public/test/android/BUILD.gn b/content/public/test/android/BUILD.gn
index 8039fc324d6254a63a295ad68bfce6f724f21b84..160b4461d917beedb3ae1012c30a8309bcb74ad8 100644
--- a/content/public/test/android/BUILD.gn
+++ b/content/public/test/android/BUILD.gn
@@ -1,7 +1,6 @@
 import("//build/config/android/config.gni")
 import("//build/config/android/rules.gni")
 
-# GYP: //content/content_tests.gypi:test_support_content_jni_headers
 generate_jni("test_support_content_jni_headers") {
   jni_package = "content/public/test"
   sources = [
@@ -17,7 +16,6 @@ android_library("layouttest_java_support") {
   java_files = [ "javatests/src/org/chromium/content/browser/test/NestedSystemMessageHandler.java" ]
 }
 
-# GYP: //content/content_tests.gypi:content_java_test_support
 android_library("content_java_test_support") {
   testonly = true
   deps = [