clean oobe mono audio setting as they are not used

chrome/browser/ui/webui/chromeos/login/core_oobe_handler.cc

Index: chrome/browser/ui/webui/chromeos/login/core_oobe_handler.cc
diff --git a/chrome/browser/ui/webui/chromeos/login/core_oobe_handler.cc b/chrome/browser/ui/webui/chromeos/login/core_oobe_handler.cc
index d437e7653f0266e0f7287ed511407edf612f1570..6d0fc58fae76ffbea0b5d0f9456cff1f2c8bcfd1 100644
--- a/chrome/browser/ui/webui/chromeos/login/core_oobe_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/core_oobe_handler.cc
@@ -88,7 +88,6 @@ void CoreOobeHandler::DeclareLocalizedValues(
   builder->Add("highContrastOption", IDS_OOBE_HIGH_CONTRAST_MODE_OPTION);
   builder->Add("screenMagnifierOption", IDS_OOBE_SCREEN_MAGNIFIER_OPTION);
   builder->Add("virtualKeyboardOption", IDS_OOBE_VIRTUAL_KEYBOARD_OPTION);
-  builder->Add("monoAudioOption", IDS_OOBE_MONO_AUDIO_OPTION);
   builder->Add("closeAccessibilityMenu", IDS_OOBE_CLOSE_ACCESSIBILITY_MENU);
 
   // Strings for the device requisition prompt.
@@ -140,8 +139,6 @@ void CoreOobeHandler::RegisterMessages() {
               &CoreOobeHandler::HandleEnableLargeCursor);
   AddCallback("enableVirtualKeyboard",
               &CoreOobeHandler::HandleEnableVirtualKeyboard);
-  AddCallback("enableMonoAudio",
-              &CoreOobeHandler::HandleEnableMonoAudio);
   AddCallback("enableScreenMagnifier",
               &CoreOobeHandler::HandleEnableScreenMagnifier);
   AddCallback("enableSpokenFeedback",
@@ -313,10 +310,6 @@ void CoreOobeHandler::HandleEnableVirtualKeyboard(bool enabled) {
   AccessibilityManager::Get()->EnableVirtualKeyboard(enabled);
 }
 
-void CoreOobeHandler::HandleEnableMonoAudio(bool enabled) {
-  AccessibilityManager::Get()->EnableMonoAudio(enabled);
-}
-
 void CoreOobeHandler::HandleEnableScreenMagnifier(bool enabled) {
   // TODO(nkostylev): Add support for partial screen magnifier.
   DCHECK(MagnificationManager::Get());