Not automatically. But you can do this in the Rails console, if the converter script has set some custom field on imported posts. This should be the case for most current importer scripts.
system_user = Discourse.system_user
PostCustomField.joins(:post).includes(:post).where(name: 'import_id').map {|pcf| pcf.post.topic_id }.sort.uniq.each do |topic_id|
PostDestroyer.new(system_user, Topic.find(topic_id).ordered_posts.first).destroy
end