Remove incomplete manual binding for TimeoutAddFull

[cameronwhite]

Now that global functions are generated, this is available as GLib.Functions.TimeoutAddFull() (the generated version works fine in my testing).

GtkSharp had a similar GLib.Timeout class so I stumbled across this while porting Pinta, and then found it didn't work :)

[cameronwhite]

Somewhat related, I noticed that https://docs.gtk.org/glib/func.timeout_add_full.html mentions This method is renamed to [g_timeout_add()](https://docs.gtk.org/glib/func.timeout_add.html) in language bindings.
So perhaps the shadows property is what indicates it should be renamed to TimeoutAdd?

[badcel]

Oh very interesting catch. This is used for method overloading which is not yet implemented. See #761