MdeModulePkg:Fix the potential memory leak issue in Display Engine

MdeModulePkg:Fix the potential memory leak issue in Display Engine

The MenuOption insert to gMenuOption allocate memory every time,but not free.
Now add the code to free it.And for Date/Time,it will create 3 menus,but previously
the Description point to the same address,so when free the Description,it will cause
issue,now reset the Description pointer.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19647 6f19259b-4bc3-4df7-8a09-765794883524