Temporarily remove validFrom/validUntil from v2 context.

Author: msporny

contexts/credentials/v2

@@ -51,7 +51,7 @@
         },
         "proof": {
           "@id": "https://w3id.org/security#proof",
-          "@type": "@id", 
+          "@type": "@id",
           "@container": "@graph"
         },
         "refreshService": {
@@ -61,14 +61,6 @@
         "termsOfUse": {
           "@id": "https://www.w3.org/2018/credentials#termsOfUse",
           "@type": "@id"
-        },
-        "validFrom": {
-          "@id": "https://www.w3.org/2018/credentials#validFrom",
-          "@type": "http://www.w3.org/2001/XMLSchema#dateTime"
-        },
-        "validUntil": {
-          "@id": "https://www.w3.org/2018/credentials#validUntil",
-          "@type": "http://www.w3.org/2001/XMLSchema#dateTime"
         }
       }
     },
@@ -90,7 +82,7 @@
         },
         "verifiableCredential": {
           "@id": "https://www.w3.org/2018/credentials#verifiableCredential",
-          "@type": "@id", 
+          "@type": "@id",
           "@container": "@graph"
         }
       }