core: Fix reference to renamed functions
core: Fix reference to renamed functions

GrlMetadataSource doesn't exist any more.

https://bugzilla.gnome.org/show_bug.cgi?id=730003

GNOME/grilo,MathieuDuponchelle/grilo,grilofw/grilo,grilofw/grilo,GNOME/grilo,MathieuDuponchelle/grilo,grilofw/grilo,jasuarez/grilo,jasuarez/grilo,MathieuDuponchelle/grilo,jasuarez/grilo