gnome-power-manager: fix compile

* on some machines help crashed with:
| xsltproc -o gnome-power-manager-C.omf --stringparam db2omf.basename gnome-power-manager --stringparam db2omf.format 'docbook' --stringparam db2omf.dtd "-//OASIS//DTD DocBook XML V4.3//EN" --stringparam db2omf.lang C --stringparam db2omf.omf_dir "/usr/share/omf" --stringparam db2omf.help_dir "/usr/share/gnome/help" --stringparam db2omf.omf_in "/home/jenkins/oe/shr-core-branches/shr-core/tmp-eglibc/work/armv5te-oe-linux-gnueabi/gnome-power-manager/2.32.0-r2/gnome-power-manager-2.32.0/help/gnome-power-manager.omf.in"  /home/jenkins/oe/shr-core-branches/shr-core/tmp-eglibc/sysroots/qemuarm`/home/jenkins/oe/shr-core-branches/shr-core/tmp-eglibc/sysroots/x86_64-linux/usr/bin/pkg-config --variable db2omf gnome-doc-utils` C/gnome-power-manager.xml || { rm -f "gnome-power-manager-C.omf"; exit 1; }
| unable to parse fr/gnome-power-manager.xml

* disable man in recipe did not work

Signed-off-by: Andreas Müller <schnitzeltony@googlemail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>