Fix DiskRP Swagger "Type doesn't exist in PrivateEndpointConnection" error (#12521)

Author: scottlzhang

specification/compute/resource-manager/Microsoft.Compute/stable/2020-09-30/disk.json

@@ -2877,18 +2877,23 @@
           "x-ms-client-flatten": true,
           "description": "Resource properties."
         },
+        "id": {
+          "readOnly": true,
+          "type": "string",
+          "description": "private endpoint connection Id"
+        },
+        "name": {
+          "readOnly": true,
+          "type": "string",
+          "description": "private endpoint connection name"
+        },
         "type": {
           "readOnly": true,
           "type": "string",
           "description": "private endpoint connection type"
         }
       },
       "description": "The Private Endpoint Connection resource.",
-      "allOf": [
-        {
-          "$ref": "#/definitions/ProxyOnlyResource"
-        }
-      ],
       "x-ms-azure-resource": true
     },
     "DiskAccessProperties": {