Provide documentation and perhaps tools to delete old records

Is it the login_history table or the lhfingerprintjs2 table that presents an issue for you?

There is no possibility to clear data from UI.

You can implement hook_cron():

/**
 * Implements hook_cron().
 */
function MODULE_cron() {
  $num_deleted = db_delete('login_history')
    ->execute();
}

The example above removes all data from login_history table.
+ you can add a condition by time
->condition('login', strtotime('-1 week'), '<')
So, you can remove only old data.

Since many of us are required to comply with the GDPR legislation where users have "the right to be forgotten", it is a good idea to provide an admin page with a select option to delete entries that are more than e.g. x months old, and maybe even an option for deleting all login history for a given user.

The pruning of the table could take place when cron is run.

Good point. Adding a GDPR tag to this to help raise that visibility.