Disable smoke testing for load:tools:stackoverflow story

This is deprecated and will be replaced by load:tools:stackoverflow:2018
story. Disabling now because we are hitting CQ capacity.

Bug: 893615
Change-Id: I29b839a0d8bfd007f36a1d09ca1e52a4620735cf
TBR: nednguyen@google.com
Reviewed-on: https://chromium-review.googlesource.com/c/1280617
Commit-Queue: Annie Sullivan <sullivan@chromium.org>
Reviewed-by: Annie Sullivan <sullivan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599806}

tools/perf/benchmarks/system_health_smoke_test.py

@@ -57,6 +57,7 @@ _DISABLED_TESTS = frozenset({
   'benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_desktop/load:news:qq',  # pylint: disable=line-too-long
   # crbug.com/893615
   'benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_desktop/load:news:cnn',  # pylint: disable=line-too-long
+  'benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_desktop/load:tools:stackoverflow',  # pylint: disable=line-too-long
   'benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_desktop/load:games:alphabetty',  # pylint: disable=line-too-long
 
   # crbug.com/698006