UefiCpuPkg PiSmmCpuDxeSmm: Remove redundant code to set IDT range to RO

UefiCpuPkg PiSmmCpuDxeSmm: Remove redundant code to set IDT range to RO

AllocateCodePages() is used to allocate buffer for IDT range,
the code pages will be set to RO in SetMemMapAttributes(),
then the code to set IDT range to RO in PatchGdtIdtMap() is
redundant and could be removed.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>