Remove lingering configuration data in block plugin
There are several options.

You can unset the configuration 'row' in submit:

unset($this-&gt;configuration['row']);


You can load each block, remove the item from settings and save it. See https://drupal.stackexchange.com/a/224362/47547 how to load blocks. You can do this in an update hook.

You can export the configuration, remove the lines you don't want from the yaml files and import the configuration again. This would be the best option for a site owner who wants to clean up a single drupal installation.