Remove the `points` value option

[wilfwilson]

I don't like the points option any more, so I'm going to remove it. It is redundant, and can be replaced by an additional constraint Constraint.MovedPoints or Constraint.LargestMovedPoint (or by simply including an integer k in the list of constraints).

Maintaining multiple ways to do the same thing is annoying.

In addition, the GAP bug described in gap-system/gap#4510 also has the potential to cause really weird behaviour in relation to the points option. This has caught me out before. So that's an added bonus.