Revert "sign_ssh_keys: Add hook to sign SSH host cert"

No longer using Step CA for SSH host certificates.  Switched to sshca.

This reverts commit e5eff964a1.

Containerfile

@@ -17,12 +17,9 @@ RUN --mount=type=cache,target=/var/cache/apt \
 RUN --mount=from=build,source=/tmp/build/dist,target=/tmp/wheels \
 	python3 -m pip install -f /tmp/wheels \
 		dch_webhooks \
-		python-multipart \
 		uvicorn \
 	&& :
 
-COPY --from=docker.io/smallstep/step-cli:0.25.0 /usr/local/bin/step /usr/local/bin/step
-
 USER 1000:1000
 
 CMD ["tini", "/usr/local/bin/uvicorn", "dch_webhooks:app"]