Remove unnecessary vocab comments

Author: iherman

vocab/credentials/v2/vocabulary.yml

@@ -97,7 +97,6 @@ property:
     defined_by: https://www.w3.org/TR/vc-data-model-2.0/#defn-credentialSubject
     domain: cred:VerifiableCredential
     range: IRI
-    comment: An entity about which claims are made.
 
   - id: digestSRI
     label: Subresource integrity digest
@@ -145,7 +144,6 @@ property:
     defined_by: https://www.w3.org/TR/vc-data-model-2.0/#defn-issuer
     domain: cred:VerifiableCredential
     range: IRI
-    comment: The value of this property must be a URL uniquely identifying the issuer.
 
   - id: refreshService
     label: Refresh service
@@ -191,7 +189,6 @@ property:
     label: Verifiable credential graph
     domain: cred:VerifiablePresentation
     range: cred:VerifiableCredentialGraph
-    comment: The value of this property identifies a <a href="#VerifiableCredentialGraph">Verifiable credential graph</a>. (Informally, it indirectly identifies a <a href="#VerifiableCredential">Verifiable credential</a> contained in a separate graph.)
 
 datatype:
   - id: sriString