ci: Remove the unused linux-sparc64 setup script

This hasn't been doing anything since e580f56 ("use `qemu-sparc64`
to run sparc64 tests") which switched away from using qemu-system via
`test-runner-linux`. Thus, remove it here.

(backport <#4763>)
(cherry picked from commit 9812d5b)

Author: tgross35

ci/docker/sparc64-unknown-linux-gnu/Dockerfile

@@ -7,9 +7,6 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
         qemu-system-sparc64 openbios-sparc seabios ipxe-qemu \
         p7zip-full cpio linux-libc-dev-sparc64-cross qemu-user
 
-COPY linux-sparc64.sh /
-RUN /linux-sparc64.sh
-
 ENV CARGO_TARGET_SPARC64_UNKNOWN_LINUX_GNU_LINKER=sparc64-linux-gnu-gcc \
     CARGO_TARGET_SPARC64_UNKNOWN_LINUX_GNU_RUNNER="qemu-sparc64 -L /usr/sparc64-linux-gnu" \
     CC_sparc64_unknown_linux_gnu=sparc64-linux-gnu-gcc \