ports/96731: textproc/docbook-utils doesn`t build

[Paweł Pękala]

 Suggested approach works for me too, but I find it rather hackish.
Looking at the Makefile of docbook-utils it seems that it needs
dockbook in version 3. But durning the build the errors indicate that
it uses dockbook 4 "headers" and from my very little knowledge about
dockbook it seems that those two versions of docbook are incompatible.
So in my opinion this needs a broader approach, sadly I don`t know
docbook internals to sugest any solution ;/