Revert "ast: Fix issue with boxes that cross zero longitude"

There are better ways to fix this issue, and this one broke other things.

This reverts commit 380a8bc825e4402a2c30c5863a636b57329eed4c.
ast: Fix issue with boxes that cross zero longitude - take 2

More work on handling uncertainty regions that a discontinuity. This
time ensure that the extent of the box on each axis of the base Frame
takes account of the possibly cyclic nature of the base Frame.