Remove seldom used tab_swtiching test cases

tools/perf/page_sets/tough_image_cases.py

Index: tools/perf/page_sets/tough_image_cases.py
diff --git a/tools/perf/page_sets/tough_image_cases.py b/tools/perf/page_sets/tough_image_cases.py
deleted file mode 100644
index 256b90e9828038b4447083381de83642c981e6c9..0000000000000000000000000000000000000000
--- a/tools/perf/page_sets/tough_image_cases.py
+++ /dev/null
@@ -1,32 +0,0 @@
-# Copyright 2014 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.
-from telemetry.page import page as page_module
-from telemetry.page import shared_page_state
-from telemetry import story
-
-
-class ToughImageCasesPage(page_module.Page):
-
-  def __init__(self, url, page_set):
-    super(ToughImageCasesPage, self).__init__(
-        url=url, page_set=page_set,
-        shared_page_state_class=shared_page_state.SharedDesktopPageState)
-
-
-class ToughImageCasesPageSet(story.StorySet):
-
-  """ A collection of image-heavy sites. """
-
-  def __init__(self):
-    super(ToughImageCasesPageSet, self).__init__()
-
-    urls_list = [
-      'http://www.free-pictures-photos.com/aviation/airplane-306.jpg',
-      ('http://upload.wikimedia.org/wikipedia/commons/c/cb/'
-       'General_history%2C_Alaska_Yukon_Pacific_Exposition%'
-       '2C_fully_illustrated_-_meet_me_in_Seattle_1909_-_Page_78.jpg')
-    ]
-
-    for url in urls_list:
-      self.AddStory(ToughImageCasesPage(url, self))