Removing old snapper configs
After moving some file-systems around I found that I had a few Snapper configs that I didn't need, so I tried to remove them:
snapper -c [myconfig] delete-config
Which resulted in errors due to the directories no longer existing.
To resolve this I deleted the config file from /etc/snapper/configs - but that then started chucking up snapshot errors on cron every hour. The final nail is in /etc/sysconfig/snapper, where the SNAPPER_CONFIGS variable lists all the alleged configs, just remove the one you want from there. Hey presto.