Fix getSimplifiedGeometry definition

The override here should match the definition in ol/geom/Geometry

src/ol/render/Feature.js

@@ -191,6 +191,14 @@ class RenderFeature {
     return this;
   }
 
+  /**
+   * @param {number} squaredTolerance Squared tolerance.
+   * @return {RenderFeature} Simplified geometry.
+   */
+  getSimplifiedGeometry(squaredTolerance) {
+    return this;
+  }
+
   /**
   * Get the feature properties.
   * @return {Object<string, *>} Feature properties.
@@ -261,12 +269,4 @@ RenderFeature.prototype.getFlatCoordinates =
     RenderFeature.prototype.getOrientedFlatCoordinates;
 
 
-/**
- * Get the feature for working with its geometry.
- * @return {RenderFeature} Feature.
- */
-RenderFeature.prototype.getSimplifiedGeometry =
-    RenderFeature.prototype.getGeometry;
-
-
 export default RenderFeature;