Refine the code in function Var_UpdateDriverOption and Var_UpdateBootOption, use the existed API(EfiBootManagerInitializeLoadOption and EfiBootManagerAddLoadOptionVariable) supplied by UefiBootManagerLib to replace the same logic in the two functions. And remove the useless code. 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>