Remove GeoJSONObject extends from GeoJSONCRS

Otherwise CRS object may have a `boox` or a `crs` property

externs/geojson.js

@@ -34,11 +34,17 @@ GeoJSONObject.prototype.crs;
 
 /**
  * @constructor
- * @extends {GeoJSONObject}
  */
 var GeoJSONCRS = function() {};
 
 
+/**
+ * CRS type. One of `link` or `name`.
+ * @type {string}
+ */
+GeoJSONCRS.prototype.type;
+
+
 /**
  * TODO: remove GeoJSONCRSCode when http://jira.codehaus.org/browse/GEOS-5996
  * is fixed and widely deployed.