Use mojo SystemTray interfaces for both mash and classic ash

ash/common/system/tray/system_tray_notifier.cc

Index: ash/common/system/tray/system_tray_notifier.cc
diff --git a/ash/common/system/tray/system_tray_notifier.cc b/ash/common/system/tray/system_tray_notifier.cc
index 3629b1bde5ff2b8785d6031453afa93459c32c73..36350d3eab8e153607e82d661ac639c53df10e82 100644
--- a/ash/common/system/tray/system_tray_notifier.cc
+++ b/ash/common/system/tray/system_tray_notifier.cc
@@ -82,22 +82,10 @@ void SystemTrayNotifier::NotifyAudioActiveInputNodeChanged() {
                     OnActiveInputNodeChanged());
 }
 
-void SystemTrayNotifier::AddClockObserver(ClockObserver* observer) {
-  clock_observers_.AddObserver(observer);
-}
-
-void SystemTrayNotifier::RemoveClockObserver(ClockObserver* observer) {
-  clock_observers_.RemoveObserver(observer);
-}
-
 void SystemTrayNotifier::NotifyRefreshClock() {
   FOR_EACH_OBSERVER(ClockObserver, clock_observers_, Refresh());
 }
 
-void SystemTrayNotifier::NotifyDateFormatChanged() {
-  FOR_EACH_OBSERVER(ClockObserver, clock_observers_, OnDateFormatChanged());
-}
-
 void SystemTrayNotifier::NotifySystemClockTimeUpdated() {
   FOR_EACH_OBSERVER(ClockObserver, clock_observers_,
                     OnSystemClockTimeUpdated());