windmove.el: Mark unused code as obsolete

windmove.el: Mark unused code as obsolete

* lisp/windmove.el (windmove-window-distance-delta)
(windmove-coord-add, windmove-constrain-to-range)
(windmove-constrain-around-range, windmove-frame-edges)
(windmove-constrain-loc-for-movement)
(windmove-wrap-loc-for-movement, windmove-reference-loc)
(windmove-other-window-loc): Declare obsolete.
(windmove-find-other-window, windmove-do-window-select):
Doc fixes.

* etc/NEWS: Document it.