Remove unused ThumbnailDatabase::UpdateIconMapping() and ThumbnailDatabase::CloneIconMappings()

components/history/core/browser/history_service.h

Index: components/history/core/browser/history_service.h
diff --git a/components/history/core/browser/history_service.h b/components/history/core/browser/history_service.h
index 7d7b00ccc4116144df7552d2a08439b84e717a51..aaab5f3c1cfbfe52b8d9de0879f2d3b9af3aa06c 100644
--- a/components/history/core/browser/history_service.h
+++ b/components/history/core/browser/history_service.h
@@ -748,10 +748,6 @@ class HistoryService : public syncer::SyncableService, public KeyedService {
   // of date.
   void SetFaviconsOutOfDateForPage(const GURL& page_url);
 
-  // Used by the FaviconService to clone favicons from one page to another,
-  // provided that other page does not already have favicons.
-  void CloneFavicons(const GURL& old_page_url, const GURL& new_page_url);
-
   // Used by the FaviconService for importing many favicons for many pages at
   // once. The pages must exist, any favicon sets for unknown pages will be
   // discarded. Existing favicons will not be overwritten.