Remove references to page_cycler_v2.tough_layout_cases (deleted bench…

…mark)

Bug: 767546
Change-Id: Ia829774573ba0c329a52055e34be77dfa6a82d52
Reviewed-on: https://chromium-review.googlesource.com/677644
Reviewed-by: Helen Li <xunjieli@chromium.org>
Commit-Queue: Ned Nguyen <nednguyen@google.com>
Cr-Commit-Position: refs/heads/master@{#503579}

tools/perf/core/desktop_benchmark_avg_times.json

@@ -9,7 +9,7 @@
     "blink_perf.dom": 98.51104682236321,
     "blink_perf.events": 66.05652102455497,
     "blink_perf.layout": 453.38422619201697,
-    "blink_perf.owp_storage": 30.0, 
+    "blink_perf.owp_storage": 30.0,
     "blink_perf.paint": 51.07198746293505,
     "blink_perf.parser": 400.27208882935196,
     "blink_perf.shadow_dom": 81.56559749378646,
@@ -56,7 +56,6 @@
     "page_cycler_v2.intl_ja_zh": 2381.6099734405675,
     "page_cycler_v2.intl_ko_th_vi": 1651.235684189815,
     "page_cycler_v2.top_10_mobile": 671.6237025374458,
-    "page_cycler_v2.tough_layout_cases": 1047.1903459546722,
     "page_cycler_v2.typical_25": 2253.314608139926,
     "page_cycler_v2_site_isolation.basic_oopif": 513.9117965158755,
     "power.steady_state": 596.0703444047408,