Remove workaround for split dosage cardinality of bounds element

[dvribeira]

Since today, building of the IG is not working because of the slicing of the boundsPeriod element.

Sushi will complain already that the rule to allow only Period slicing for bounds[x] cannot be applied because Period is not a valid type. This comes from the fact that in the dosage split resource definition upstream (CH EMED), the boundsPeriod slice is not allowed, but the other slices are. How come this was not an issue before and now it is, remains a bit of a mistery but it is in any case irrelevant since the main issue in the end is the cardinality of the bounds[x] element as a whole in the split dosage profile. See hl7ch/ch-emed#309

This forces us to split the enforcement of the Period type so that it is not applied to split dosage and to also enforce the 0..0 cardinality on the whole element for the split dosage ourselves until this is applied upstream. Once this is applied upstream, we should remove the redundant cardinality rule on the split dosage profile.