Eliminate unnecessary conversion from cursor steps to range
Remove unnecessary (and impossible to use) constraint argument

The constraint function only allows a choice between two adjacent steps
if the supplied position is not exactly on a step. With things such as
inline roots and other complex features of the addressing system, this
is extremely difficult to use correctly.

As it is currently unused, the best thing to prevent future problems it
to terminate it now!
Remove unnecessary test returns (again!)

These were just cleaned up, and here someone has gone and reintroduced
them again! What gives!