Documentation of how an unused feature is broken.

The feature in question (the AI using speculative unit maps) is
probably better handled a different way, which would allow a layer of
overhead to be removed. I'll leave it up to the AI folks to decide
how to proceed.


git-svn-id: http://svn.gna.org/svn/wesnoth/trunk@56360 75b3775d-3801-0410-9e12-e2e43121521d