deps: remove archs/aix64-gcc

This arch was renamed to clarify that it used the aix assembler (as) and
not the gnu assembler. It was removed from the Makefile and not being
built but would still be picked up by make targets like the header-tar
target.

PR-URL: #42616
Fixes: #42081
Refs: openssl/openssl@178fa72ed5
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Richard Lau <[email protected]>

Author: danbev