SecurityPkg: Fix wrong calculation of ImageExeInfoEntrySize

SecurityPkg: Fix wrong calculation of ImageExeInfoEntrySize

Per UEFI spec, EFI_IMAGE_EXECUTION_INFO structure is updated to comment
Signature field. So, its structure doesn't include Signature field. But,
ImageExeInfoEntrySize uses its structure size minor Signature size. It
will be corrected in this change.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Chao Zhang <chao.b.zhang@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17687 6f19259b-4bc3-4df7-8a09-765794883524