Remove usage of FOR_EACH_OBSERVER macro in ash/common

ash/common/system/chromeos/network/vpn_delegate.cc

Index: ash/common/system/chromeos/network/vpn_delegate.cc
diff --git a/ash/common/system/chromeos/network/vpn_delegate.cc b/ash/common/system/chromeos/network/vpn_delegate.cc
index df37000b8fca459488bdacc52ba4c61f99a0fe9c..00eb3e26c8314338d0463641380921b5737bc5e4 100644
--- a/ash/common/system/chromeos/network/vpn_delegate.cc
+++ b/ash/common/system/chromeos/network/vpn_delegate.cc
@@ -48,7 +48,8 @@ void VPNDelegate::RemoveObserver(Observer* observer) {
 }
 
 void VPNDelegate::NotifyObservers() {
-  FOR_EACH_OBSERVER(Observer, observer_list_, OnVPNProvidersChanged());
+  for (auto& observer : observer_list_)
+    observer.OnVPNProvidersChanged();
 }
 
 }  // namespace ash