Remove original handling on ol.Feature

This is another attempt to bring master closer to the
vector-api branch. In anticipation of the ability to keep track
of modifications on ol.Object through a beforechange event
(d7e4be0), we will be able to manage originals on the
application level or in a separate component outside of
ol.Feature.

src/ol/feature.js

@@ -42,13 +42,6 @@ ol.Feature = function(opt_values) {
    */
   this.geometryName_;
 
-  /**
-   * Original of this feature when it was modified.
-   * @type {ol.Feature}
-   * @private
-   */
-  this.original_ = null;
-
   /**
    * The render intent for this feature.
    * @type {ol.FeatureRenderIntent|string}
@@ -114,15 +107,6 @@ ol.Feature.prototype.getGeometry = function() {
 };
 
 
-/**
- * Get the original of this feature when it was modified.
- * @return {ol.Feature} Original.
- */
-ol.Feature.prototype.getOriginal = function() {
-  return this.original_;
-};
-
-
 /**
  * Get any symbolizers set directly on the feature.
  * @return {Array.<ol.style.Symbolizer>} Symbolizers (or null if none).
@@ -198,15 +182,6 @@ ol.Feature.prototype.setGeometry = function(geometry) {
 };
 
 
-/**
- * Set the original of this feature when it was modified.
- * @param {ol.Feature} original Original.
- */
-ol.Feature.prototype.setOriginal = function(original) {
-  this.original_ = original;
-};
-
-
 /**
  * Gets the renderIntent for this feature.
  * @return {string} Render intent.