MdeModulePkg: remove PE/COFF header workaround for ELILO on IPF

Now that Itanium support has been dropped, we can remove the various
occurrences of the ELILO on Itanium PE/COFF header workaround.

Link: https://bugzilla.tianocore.org/show_bug.cgi?id=816
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>