[Mac] Delete more bookmark bar folder code. This removes things that were missed last time.

chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_button_cell.mm

-// Copyright (c) 2011 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 "chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_button_cell.h"
-
-@implementation BookmarkBarFolderButtonCell
-
-+ (id)buttonCellForNode:(const BookmarkNode*)node
-            contextMenu:(NSMenu*)contextMenu
-               cellText:(NSString*)cellText
-              cellImage:(NSImage*)cellImage {
-  id buttonCell =
-      [[[BookmarkBarFolderButtonCell alloc] initForNode:node
-                                            contextMenu:contextMenu
-                                               cellText:cellText
-                                              cellImage:cellImage]
-       autorelease];
-  return buttonCell;
-}
-
-- (BOOL)isFolderButtonCell {
-  return YES;
-}
-
-- (void)setMouseInside:(BOOL)flag animate:(BOOL)animated {
-}
-
-@end