No longer produce md5, sha1 + sha512 checksums, but only sha256

We no longer rely on those checksum files and it increases build
time. It should be enough to generate just the sha256 checksum file.

Related to https://github.com/grml/grml/issues/120

diff --git a/grml-live b/grml-live
index 8b0adfe..9a78995 100755 (executable)
--- a/grml-live
+++ b/grml-live
@@ -1582,14 +1582,8 @@ else
          [ "$RC" = 0 ] && \
          (
            if cd $ISO_OUTPUT ; then
          [ "$RC" = 0 ] && \
          (
            if cd $ISO_OUTPUT ; then

-             md5sum ${ISO_NAME} > ${ISO_NAME}.md5 && \
-             touch -r ${ISO_NAME} ${ISO_NAME}.md5
-             sha1sum ${ISO_NAME} > ${ISO_NAME}.sha1 && \
-             touch -r ${ISO_NAME} ${ISO_NAME}.sha1

              sha256sum ${ISO_NAME} > ${ISO_NAME}.sha256 && \
              touch -r ${ISO_NAME} ${ISO_NAME}.sha256
              sha256sum ${ISO_NAME} > ${ISO_NAME}.sha256 && \
              touch -r ${ISO_NAME} ${ISO_NAME}.sha256

-             sha512sum ${ISO_NAME} > ${ISO_NAME}.sha512 && \
-             touch -r ${ISO_NAME} ${ISO_NAME}.sha512

            fi
          )
          ;;
            fi
          )
          ;;