Since beginning of june 2017, I have the directory ...
Shall I leave it or delete it?What is it for?Who created it?
Yes I have it also.
Seems like we should keep it !
Yeah, keep that the acme-challenge is part of the acme protocol used by Let's Encrypt. This article has a nice explanation for it: https://ma.ttias.be/well-known-directory-webservers-aka-rfc-5785/