gtkbin: Remove the silliest code on earth

gtkbin: Remove the silliest code on earth

What is this bin doing with all these crazy deltas? Company does:

<Company> that can safely be removed
<Company> in general, code that isn't obvious can either be understood
<Company> with a bit of thinking or it can be removed
<Company> if in doubt, go for the 2nd of those :)

Most GtkBin subclasses override this strange garbage anyway, so it's
not like this code is ever *run*, per se. Just make it proxy directly
to the child, and hope nothing goes wrong.