Remove som GYP annotations, remove unused manifest.

device/serial/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/features.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 
 # Library works only on desktop platforms.
 assert(is_win || is_linux || is_mac)
 
 config("platform_support") {
   visibility = [ ":serial" ]
   if (is_win) {
     libs = [ "setupapi.lib" ]
     ldflags = [ "/DELAYLOAD:setupapi.dll" ]
   }
 }
 
-# GYP version: device/serial/serial.gyp:device_serial
 static_library("serial") {
   output_name = "device_serial"
 
   sources = [
     "buffer.cc",
     "buffer.h",
     "data_receiver.cc",
     "data_receiver.h",
     "data_sender.cc",
     "data_sender.h",
@@ skipping 47 matching lines @@
     ]
   }
   if (is_mac) {
     libs = [
       "Foundation.framework",
       "IOKit.framework",
     ]
   }
 }
 
-# GYP version: device/serial/serial.gyp:device_serial_test_util
 static_library("test_support") {
   sources = [
     "test_serial_io_handler.cc",
     "test_serial_io_handler.h",
   ]
 
   public_deps = [
     ":serial",
   ]
 }
 
-# GYP version: device/serial/serial.gyp:device_serial_mojo
 mojom("serial_mojo") {
   visibility = [
     ":serial",
     "//extensions:extensions_renderer_resources_grit",
   ]
 
   sources = [
     "data_stream.mojom",
     "data_stream_serialization.mojom",
     "serial.mojom",
     "serial_serialization.mojom",
   ]
 
   use_new_wrapper_types = false
 }