Change MEDDRA ID semantic type to Disease

Making it Biolink Disease for now, since we have more support for mapping to other IDs through MyDisease (see [comment](biothings/biothings_explorer#217 (comment))).

mychem.info/openapi_full.yml

@@ -734,7 +734,7 @@ components:
         semantic: ChemicalSubstance
       outputs:
       - id: MEDDRA
-        semantic: PhenotypicFeature
+        semantic: Disease
       predicate: causes_adverse_event  ## current biolink predicate
       ## through drugcentral, FDA Adverse Event Reporting System (FAERS) information
       source: drugcentral
@@ -756,7 +756,7 @@ components:
         semantic: ChemicalSubstance
       inputs:
       - id: MEDDRA
-        semantic: PhenotypicFeature
+        semantic: Disease
       predicate: adverse_event_caused_by  ## current biolink predicate
       source: drugcentral
       response_mapping: