vala: remove custom code for media getters/setters
vala: remove custom code for media getters/setters

With the new functions the introspection mechanism can detect
the those symbols. No need to add them manually anymore.

Signed-off-by: Víctor Manuel Jáquez Leal <853e0dbb5ddd43a0f0483f24794ae05c4c52af91@igalia.com>

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