Remove som GYP annotations, remove unused manifest.

chromecast/base/component/BUILD.gn

 # Copyright 2016 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("//chromecast/chromecast.gni")
 import("//testing/test.gni")
 
-# GYP target: chromecast.gyp:cast_component
 source_set("component") {
   sources = [
     "component.cc",
     "component.h",
     "component_internal.h",
   ]
 
   deps = [
     "//base",
   ]
 }
 
-# GYP target: chromecast_tests.gypi:cast_component_unittests
 test("cast_component_unittests") {
   sources = [
     "component_unittest.cc",
   ]
 
   deps = [
     ":component",
     "//base",
     "//base/test:run_all_unittests",
     "//testing/gtest",
   ]
 }