MdeModulePkg: Use EfiEventEmptyFunction from UefiLib

Use EfiEventEmptyFunction from UefiLib and remove the duplication
of event empty function.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=298

Cc: Feng Tian <feng.tian@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>

MdeModulePkg/Core/Dxe/DxeMain.h

@@ -2,7 +2,7 @@
   The internal header file includes the common header files, defines
   internal structure and functions used by DxeCore module.
 
-Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2006 - 2017, Intel Corporation. All rights reserved.<BR>
 This program and the accompanying materials
 are licensed and made available under the terms and conditions of the BSD License
 which accompanies this distribution.  The full text of the license may be found at
@@ -2675,22 +2675,6 @@ CoreReleaseLock (
   IN EFI_LOCK  *Lock
   );
 
-
-/**
-  An empty function to pass error checking of CreateEventEx ().
-
-  @param  Event                 Event whose notification function is being invoked.
-  @param  Context               Pointer to the notification function's context,
-                                which is implementation-dependent.
-
-**/
-VOID
-EFIAPI
-CoreEmptyCallbackFunction (
-  IN EFI_EVENT                Event,
-  IN VOID                     *Context
-  );
-
 /**
   Read data from Firmware Block by FVB protocol Read. 
   The data may cross the multi block ranges.