Remove unused method declaration from io_thread.h

io_thread's GetNetworkServiceOnUIThread() is removed in r525444.
This is to update the header file.

R=mmenke@chromium.org

Change-Id: I0ce2f34c68c333fa1a525952d43f6058329afe11
Reviewed-on: https://chromium-review.googlesource.com/895803
Commit-Queue: Helen Li <xunjieli@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533329}

chrome/browser/io_thread.h

@@ -214,13 +214,6 @@ class IOThread : public content::BrowserThreadDelegate {
   // Configures |builder|'s ProxyResolutionService based on prefs and policies.
   void SetUpProxyService(network::URLRequestContextBuilderMojo* builder) const;
 
-  // Gets a pointer to the NetworkService. Can only be called on the UI thread.
-  // When out-of-process NetworkService is enabled, this is a reference to the
-  // NetworkService created through ServiceManager; when out-of-process
-  // NetworkService is not enabld, this is a Mojo interface to the IOThread's
-  // in-process NetworkService that lives on the IO thread.
-  network::mojom::NetworkService* GetNetworkServiceOnUIThread();
-
   certificate_transparency::TreeStateTracker* ct_tree_tracker() const;
 
  private: