Remove unused ol.format.Feature.getExtensions function

src/ol/format/geojson.js

@@ -57,14 +57,6 @@ ol.format.GeoJSON = function(opt_options) {
 ol.inherits(ol.format.GeoJSON, ol.format.JSONFeature);
 
 
-/**
- * @const
- * @type {Array.<string>}
- * @private
- */
-ol.format.GeoJSON.EXTENSIONS_ = ['.geojson'];
-
-
 /**
  * @param {GeoJSONGeometry|GeoJSONGeometryCollection} object Object.
  * @param {olx.format.ReadOptions=} opt_options Read options.
@@ -334,14 +326,6 @@ ol.format.GeoJSON.GEOMETRY_WRITERS_ = {
 };
 
 
-/**
- * @inheritDoc
- */
-ol.format.GeoJSON.prototype.getExtensions = function() {
-  return ol.format.GeoJSON.EXTENSIONS_;
-};
-
-
 /**
  * Read a feature from a GeoJSON Feature source.  Only works for Feature or
  * geometry types.  Use {@link ol.format.GeoJSON#readFeatures} to read