In 5c66f954 (Allow to configure gitlab socket just by path) we added
gitlab_socket option to allow users to configure path to Unicorn socket
just by path.

But @jacobvosmaer asks for even more - make http+unix:// stuff internal
and not even try to confuse users with e.g. description of URL-encoding
socket path and possibility to configure sockets with gitlab_url and
just direct unconditionally to gitlab_socket for that case.

So be it - for users it is now shown that the only way to configure
sockets is via gitlab_socket option. Internally we still use
http+unix:// scheme and handle it even if it is given in gitlab_url.