Revert "//tools/perf: Disable story on smoothness benchmark"

This reverts commit b2aea62a.

Reason for revert: The offending change has been reverted on https://chromium-review.googlesource.com/c/chromium/src/+/699755.

Original change's description:
> //tools/perf: Disable story on smoothness benchmark
> 
> TBR=rnephew
> 
> Bug: 771368
> Change-Id: Ic194b890084702105f00b9246b1971f9062dbf2f
> Reviewed-on: https://chromium-review.googlesource.com/699312
> Reviewed-by: Stephen Martinis <martiniss@chromium.org>
> Reviewed-by: rnephew <rnephew@chromium.org>
> Commit-Queue: Stephen Martinis <martiniss@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#506228}

TBR=rnephew@chromium.org,martiniss@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 771368
Change-Id: I3de10e67b4ab36c08d1a82ab4e8fcef226295037
Reviewed-on: https://chromium-review.googlesource.com/701316Reviewed-by: rnephew <rnephew@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506637}

tools/perf/benchmarks/smoothness.py

@@ -96,9 +96,7 @@ class SmoothnessToughPathRenderingCases(_Smoothness):
   def GetExpectations(self):
     class StoryExpectations(story_module.expectations.StoryExpectations):
       def SetExpectations(self):
-        self.DisableStory('IE Chalkboard',
-                          [story_module.expectations.ALL],
-                          'crbug.com/771368')
+        pass # Nothing.
     return StoryExpectations()