Remove unnecessary "export" in PowerMonitorBroadcastSource

device/power_monitor/public/cpp/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("//build/config/features.gni")
 
 source_set("cpp") {
   sources = [
-    "//device/power_monitor/power_monitor_export.h",
     "power_monitor_broadcast_source.cc",
     "power_monitor_broadcast_source.h",
   ]
 
-  defines = [ "DEVICE_POWER_MONITOR_IMPLEMENTATION" ]
-
   deps = [
     "//base",
     "//mojo/public/cpp/bindings",
     "//services/service_manager/public/cpp",
   ]
 
   public_deps = [
     "//device/power_monitor/public/interfaces",
   ]
 }