Drop "description" from content{MediaType,Encoding} in meta-schema

None of other keywords have a description.

Author: dlax

schema.json

@@ -152,14 +152,8 @@
             ]
         },
         "format": { "type": "string" },
-        "contentMediaType": {
-            "type": "string",
-            "description": "A media type, as described in RFC 2046"
-        },
-        "contentEncoding": {
-            "type": "string",
-            "description": "A content encoding scheme, as described in RFC 2045"
-        },
+        "contentMediaType": { "type": "string" },
+        "contentEncoding": { "type": "string" },
         "if": {"$ref": "#"},
         "then": {"$ref": "#"},
         "else": {"$ref": "#"},