mash: Change CastConfigDelegate to a mojoified CastConfigClient.

ash/common/system/tray/system_tray_delegate.h

Index: ash/common/system/tray/system_tray_delegate.h
diff --git a/ash/common/system/tray/system_tray_delegate.h b/ash/common/system/tray/system_tray_delegate.h
index 20a1b4f6de8a85156d2e82b8c227425e0907bf6f..6c8a20fcb48e60c24d26a5957bea561c4e1eb112 100644
--- a/ash/common/system/tray/system_tray_delegate.h
+++ b/ash/common/system/tray/system_tray_delegate.h
@@ -69,7 +69,6 @@ struct ASH_EXPORT UpdateInfo {
   bool factory_reset_required;
 };
 
-class CastConfigDelegate;
 class NetworkingConfigDelegate;
 
 // SystemTrayDelegate is intended for delegating tasks in the System Tray to the
@@ -184,9 +183,6 @@ class ASH_EXPORT SystemTrayDelegate {
   // Returns whether the delegate has initiated a bluetooth discovery session.
   virtual bool GetBluetoothDiscovering();
 
-  // Returns CastConfigDelegate. May return nullptr.
-  virtual CastConfigDelegate* GetCastConfigDelegate();
-
   // Returns NetworkingConfigDelegate. May return nullptr.
   virtual NetworkingConfigDelegate* GetNetworkingConfigDelegate() const;