- mzdyn3m.lo no longer gets built for s390x, remove it from %files

Notes:
- unfortunately the build in my home repo runs into a timeout, but you can find the "file not found" message leading to this SR in openSUSE:Factory:zSystems build log: https://build.opensuse.org/package/live_build_log/openSUSE:Factory:zSystems/racket/standard/s390x
- ppc fails to build for a different reason, therefore I restricted this change to only s390x. I don't know if mzdyn3m.lo still gets built for ppc - that's something to check after someone fixes the first ppc build failure.