core: removed wrong free at GrlMediaPlugin finalize()
core: removed wrong free at GrlMediaPlugin finalize()

GrlPluginInfo id can't be freed as it's assigned from a string in the heap.

b.g.o. #627207

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