MdeModulePkg/BMMUiLib: Remove old useless data before new save action

There exits the case that when saving changes in form A,
the old saved data in form B are not cleaned, will be saved
again with the new save. Thus incorrect UI behavior will be
shown. This patch is to remove some useless data.

https://bugzilla.tianocore.org/show_bug.cgi?id=385

Cc: Eric Dong <eric.dong@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>

MdeModulePkg/Library/BootMaintenanceManagerUiLib/BootMaintenanceManager.h

@@ -1,7 +1,7 @@
 /** @file
 Header file for boot maintenance module.
 
-Copyright (c) 2004 - 2016, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2004 - 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
@@ -1049,6 +1049,18 @@ DiscardChangeHandler (
   IN  BMM_FAKE_NV_DATA                *CurrentFakeNVMap
   );
 
+
+/**
+  This function is to clean some useless data before submit changes.
+
+  @param Private            The BMM context data.
+
+**/
+VOID
+CleanUselessBeforeSubmit (
+  IN  BMM_CALLBACK_DATA               *Private
+  );
+
 /**
   Dispatch the display to the next page based on NewPageId.