Add action to delete specific field values

It would be nice if this module provided an action that allowed for bulk deletion of specific field values - for instance, you may want to remove all instances of two taxonomy terms in a muiltivalue taxonomy term field, or all instances of a specific string from a textfield.

This is related to #1421656: Extend the "modify entity values" action to add a delete mode for multiple-value properties and fields → , but for Drupal 8. Unlike the other issue, I thought it would make sense to have delete be a separate action, in case more logic needs to be tweaked specifically for deleting values.