zypper pa --unneeded | grep '^i' | cut -d\\| -f3 | xargs sudo zypper -n remove

• zypper pa --unneeded lists unneeded packages.
• grep '^i' selects lines that starts with i (installed package)
• cut d\\| -f3 selects third field after cutting line at delimited |
• And the last one runs sudo zypper -n remove on the output.

On older version of zypper, following script may be useful

https://github.com/dilawar/Scripts/blob/master/zypper_autoremove.sh