Remove getSimplifiedGeometry from ol.geom.Circle

The `getSimplifiedGeometry` method is unnecessary as
`ol.geom.SimpleGeometry`'s default implementation is to do the
same thing (return `this`).

src/ol/geom/circle.js

@@ -129,15 +129,6 @@ ol.geom.Circle.prototype.getRadiusSquared_ = function() {
 };
 
 
-/**
- * @inheritDoc
- * @todo api
- */
-ol.geom.Circle.prototype.getSimplifiedGeometry = function(squaredTolerance) {
-  return this;
-};
-
-
 /**
  * @inheritDoc
  * @todo api