Bug 15303 Followup for koha-remove

Bug 15303 Followup for koha-remove

This patch makes koha-remove take care of

/etc/letsencrypt/renewal/$opacdomain.conf
/var/lib/koha/$site/letsencrypt.enabled

It also adds a few helper functions.

To test
- create a koha instance with LE
- observe you got both files mentioned above
- remove that instance
- verify the files are gone

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>