Remove an unused include from chrome/browser/chromeos/audio

BUG=437700
TEST=everything builds as before

Review URL: https://codereview.chromium.org/790603006

Cr-Commit-Position: refs/heads/master@{#308235}

chrome/browser/chromeos/audio/audio_devices_pref_handler_impl.cc

@@ -13,7 +13,6 @@
 #include "base/prefs/pref_service.h"
 #include "base/prefs/scoped_user_pref_update.h"
 #include "base/strings/string_number_conversions.h"
-#include "chrome/browser/chrome_notification_types.h"
 #include "chrome/common/pref_names.h"
 #include "chromeos/audio/audio_device.h"