Remove unused feedback class in dom distiller component

components/dom_distiller/content/browser/external_feedback_reporter.h

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef COMPONENTS_DOM_DISTILLER_CONTENT_BROWSER_EXTERNAL_FEEDBACK_REPORTER_H_
-#define COMPONENTS_DOM_DISTILLER_CONTENT_BROWSER_EXTERNAL_FEEDBACK_REPORTER_H_
-
-#include "base/macros.h"
-#include "content/public/browser/web_contents.h"
-#include "url/gurl.h"
-
-namespace dom_distiller {
-
-// ExternalFeedbackReporter handles reporting distillation quality through an
-// external source.
-class ExternalFeedbackReporter {
- public:
-  ExternalFeedbackReporter() {}
-  virtual ~ExternalFeedbackReporter() {}
-
-  // Start an external form to record user feedback.
-  virtual void ReportExternalFeedback(content::WebContents* web_contents,
-                                      const GURL& url,
-                                      const bool good) = 0;
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(ExternalFeedbackReporter);
-};
-
-}  // namespace dom_distiller
-
-#endif  // COMPONENTS_DOM_DISTILLER_CONTENT_BROWSER_EXTERNAL_FEEDBACK_REPORTER_H_