MdeModulePkg/Core/Dxe/Gcd: remove set but not used variables

MdeModulePkg/Core/Dxe/Gcd: remove set but not used variables

These trip up compilation with gcc.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Star Zeng <star.zeng@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18515 6f19259b-4bc3-4df7-8a09-765794883524