Update vulnerability ratings description in XML and Protobuf schemas, and revert extension changes

Signed-off-by: fahed dorgaa <fahed.dorgaa@gmail.com>

Author: fahedouch

schema/ext/vulnerability-1.0-SNAPSHOT.schema.json

@@ -146,7 +146,7 @@
         "ratings": {
           "type": "array",
           "title": "Ratings",
-          "description": "List of vulnerability ratings. Consumers SHOULD use ratings and SHOULD NOT ignore them; source ratings may differ and aid prioritization.",
+          "description": "List of the vulnerability ratings as defined by various risk rating methodologies.",
           "items": {"$ref": "#/definitions/rating"}
         },
         "cwes": {