Release process: don't pass --debug to copy-iuks-to-rsync-server-and-verify

Debug info is only useful when working on that script or to debug failures.
Let's use a terser output in the default case.

wiki/src/contribute/release_process.mdwn

@@ -858,7 +858,6 @@ Verify that Jenkins reproduced your IUKs
     "${RELEASE_CHECKOUT:?}"/bin/copy-iuks-to-rsync-server-and-verify \
        --hashes-file "${IUKS_HASHES:?}" \
        --work-dir /srv/tmp \
-       --debug \
        --jenkins-build-id "${CANDIDATE_JENKINS_IUKS_BUILD_ID:?}"
 
 If this verification succeeds, move on to the next section.