modpost: remove unused Elf_Sword macro

Commit 9ad21c3f ("kbuild: try harder to find symbol names in
modpost") added Elf_Sword (in a wrong way), but did not use it at all.

BTW, the current code looks weird.

The fix for the 32-bit part would be:

    Elf64_Sword  -->  Elf32_Sword

(inconsistet prefix, Elf32_ vs Elf64_)

The fix for the 64-bit part would be:

    Elf64_Sxword  -->  Elf64_Sword

(the size is different between Sword and Sxword)

Note:

    Elf32_Sword   ==  Elf64_Sword   ==  int32_t
    Elf32_Sxword  ==  Elf64_Sxword  ==  int64_t

Anyway, let's drop unused code instead of fixing it.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>