Consider removing NumberUtils.getDefaultValue

[ctrueden]

We probably no longer need this method, as there is now a more general ModuleService#getDefaultValue(ModuleItem) method. Of course, you might want this method in non-Module-related situations, but so far in the core software stack we don't.

If we do remove that method, we should also change the behavior of NumberUtils#clampToRange to not handle the value == null case—nothing in the core stack calls into it with a null value anyway.