Removing one of the pairing rules assertions: Generating FHIR-HF with an undefined onsetDate, when HF was reported on a follow-up assessment, and the assessment date is not available. Address issue #19

Removing one of the pairing rules assertions: Generating FHIR-HF with an undefined onsetDate, when HF was reported on a follow-up assessment, and the assessment date is not available. Address issue #19 #1