gdbus-codegen: Use C array instead of GValueArray

GValueArray was deprecated in bug 667228 and since we never change the
size of the array, it was kinda dumb to just GValueArray in the first
place.

https://bugzilla.gnome.org/show_bug.cgi?id=667228



Signed-off-by: David Zeuthen <davidz@redhat.com>