elf: Remove AArch64 from comment for AT_MINSIGSTKSZ

Remove AArch64 from comment for AT_MINSIGSTKSZ to match

commit 7cd60e43a6def40ecb75deb8decc677995970d0b
Author: Chang S. Bae <chang.seok.bae@intel.com>
Date:   Tue May 18 13:03:15 2021 -0700

    uapi/auxvec: Define the aux vector AT_MINSIGSTKSZ

    Define AT_MINSIGSTKSZ in the generic uapi header. It is already used
    as generic ABI in glibc's generic elf.h, and this define will prevent
    future namespace conflicts. In particular, x86 is also using this
    generic definition.

in Linux kernel 5.14.