Cleanup ContentSuggestions, removing unused functions

ios/chrome/browser/content_suggestions/content_suggestions_coordinator.mm

 // Copyright 2017 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.
 
 #import "ios/chrome/browser/content_suggestions/content_suggestions_coordinator.h"
 
 #include "base/mac/scoped_nsobject.h"
 #include "base/strings/sys_string_conversions.h"
 #import "ios/chrome/browser/content_suggestions/content_suggestions_mediator.h"
 #include "ios/chrome/browser/ntp_snippets/ios_chrome_content_suggestions_service_factory.h"
@@ skipping 75 matching lines @@
 }
 
 #pragma mark - ContentSuggestionsCommands
 
 - (void)openReadingList {
 }
 
 - (void)openFirstPageOfReadingList {
 }
 
-- (void)addEmptyItem {
-}
-
 - (void)openFaviconAtIndex:(NSInteger)index {
 }
 
 - (void)openURL:(const GURL&)URL {
   // TODO(crbug.com/691979): Add metrics.
 
   [self.URLLoader loadURL:URL
                  referrer:web::Referrer()
                transition:ui::PAGE_TRANSITION_AUTO_BOOKMARK
         rendererInitiated:NO];
@@ skipping 66 matching lines @@
                             appendTo:kLastTab];
 
   [self stop];
 }
 
 - (void)removeEntry {
   // TODO(crbug.com/691979): Add metrics.
 }
 
 @end