relax Condition.clinicalStatus constraint

FHIR Core is careful to limit the clinicalStatus requirement to "problem-list" items, i.e., ongoing problems, and not to make implementers guess at the clinical status of an encounter diagnosis. The US Core constraint in 10.87.1.1 (The status element has the following constraints: SHALL be present if verification status is not entered-in-error and SHALL NOT be present if verification Status is entered-in-error.) means that the VA cannot provide encounter diagnoses in FHIR. It also makes the inclusion of encounter-diagnosis in the category value set pointless.