gstreamer-1.0: Fix direction of GLib.Value typed parameters

gstreamer-1.0: Fix direction of GLib.Value typed parameters

Use `out` for functions that take an uninitialized GLib.Value.
Use `ref` for functions that take a GLib.Value initialized with
a particular type.

Remove unused Gst.ControlBindingConvert

Note that the destination is nullable, but not expressly marked as such,
in gst_value_intersect, gst_value_subtract and
gst_message_parse_property_notify.

Fixes https://gitlab.gnome.org/GNOME/vala/issues/1014