libgnurl: 7.54.1 -> 7.61.1. (#48792)

* libgnurl: 7.54.1 -> 7.61.1.

- fetch url updated (the mirror on gnunet.org seems no longer
maintained).
- most configure flags are not needed anymore since version 7.56.1 as
announced in the README
- flags -- without-ca-bundle and --with-ca-fallback are needed for
finding the CA certificates
- dependencies updated (copied from the guix package)
- license corrected

* libgnurl: fix idn support; use mirror url; add http2 support