gnu: gnunet: Update to 0.11.8.

* gnu/packages/gnunet.scm: Update to 0.11.8.
[inputs]: Add libidn2, miniupnpc, zbar. Remove glib, gmp,
gst-plugins-base, libidn, nss, openssl, perl, python-2.
[native-inputs]: Add python, xxd, which.
[arguments]: Remove configure-flags. Add phase to remove network
dependent tests. Re-arrange location of new 'check phase.