sources: remove a harmless warning message
sources: remove a harmless warning message

GConf warns if there are no writable databases in use.  Stop it from
doing that.

https://bugzilla.gnome.org/show_bug.cgi?id=671581

GNOME/gconf,hyperair/gconf-gdbus,hyperair/gconf-gdbus,hyperair/gconf-gdbus,GNOME/gconf,GNOME/gconf,hyperair/gconf-gdbus,GNOME/gconf