toolbx: Remove the SHELL instruction.

There aren't any more pipes in the Dockerfile so it's not needed and
it's ignored by Podman.

toolbx/Dockerfile

@@ -3,7 +3,6 @@ RUN go install github.com/1player/host-spawn@v1.6.0
 
 FROM docker.io/debian:testing-backports
 COPY --from=golang /go/bin/host-spawn /usr/local/bin/host-spawn
-SHELL ["/bin/bash", "-o", "pipefail", "-xc"]
 ADD [ "https://www.shore.co.il/blog/static/runas", "/usr/local/sbin/runas" ]
 COPY --chown=root:root .curlrc /root/
 # hadolint ignore=DL3008