Remove som GYP annotations, remove unused manifest.

content/public/test/android/BUILD.gn

 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 = [
     "javatests/src/org/chromium/content/browser/test/NestedSystemMessageHandler.java",
   ]
 }
 
 android_library("layouttest_java_support") {
   testonly = true
   deps = [
     "//base:base_java",
   ]
   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 = [
     ":layouttest_java_support",
     "//base:base_java",
     "//base:base_java_test_support",
     "//content/public/android:content_java",
     "//device/geolocation:geolocation_java_test_support",
   ]
   java_files = [
@@ skipping 12 matching lines @@
     "javatests/src/org/chromium/content/browser/test/util/RenderProcessLimit.java",
     "javatests/src/org/chromium/content/browser/test/util/TestCallbackHelperContainer.java",
     "javatests/src/org/chromium/content/browser/test/util/TestContentViewClient.java",
     "javatests/src/org/chromium/content/browser/test/util/TestInputMethodManagerWrapper.java",
     "javatests/src/org/chromium/content/browser/test/util/TestTouchUtils.java",
     "javatests/src/org/chromium/content/browser/test/util/TestWebContentsObserver.java",
     "javatests/src/org/chromium/content/browser/test/util/TouchCommon.java",
     "javatests/src/org/chromium/content/browser/test/util/UiUtils.java",
   ]
 }