package/gupnp: disable documentation

package/gupnp: disable documentation

gupnp always builds man page since version 1.2.3 and
https://gitlab.gnome.org/GNOME/gupnp/-/commit/23f54c2a1e8718e836224d68dafded091604a677

This will raise the following build failure on some of our autobuilders:

FAILED: doc/gupnp-binding-tool-1.2.1
/usr/bin/xsltproc --nonet --xinclude --path /home/naourr/work/instance-0/output-1/build/gupnp-1.2.3/doc:/home/naourr/work/instance-0/output-1/build/gupnp-1.2.3/build/doc --stringparam man.output.quietly 1 --stringparam funcsynopsis.style ansi --stringparam man.th.extra1.suppress 1 --stringparam man.authors.section.enabled 1 --stringparam man.copyright.section.enabled 1 -o doc/gupnp-binding-tool-1.2.1 http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl ../doc/gupnp-binding-tool.xml
I/O error : Attempt to load network entity http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl
warning: failed to load external entity "http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl"
cannot parse http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl

This issue has been reported upstream, until we got more feedback, just
revert the commit

Fixes:
 - http://autobuild.buildroot.org/results/7bf388e81dff3875e396a228b2d48d345377b0da

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>