Revert "Disable Flaky SystemHealthBenchmarkSmokeTest."

This reverts commit c6c7cdfc.

Reason for revert: Wrong story was disabled.

Original change's description:
> Disable Flaky SystemHealthBenchmarkSmokeTest.
>
> BUG=852888
>
> TBR=perezju@chromium.org
>
> Change-Id: I773594071fb0e9357af63d3024dd71125cad9723
> Reviewed-on: https://chromium-review.googlesource.com/1104880
> Reviewed-by: Steven Holte <holte@chromium.org>
> Commit-Queue: Steven Holte <holte@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#568140}

TBR=holte@chromium.org

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

NOTRY=True

Bug: 852888
Change-Id: Ibded1b8ca4185a53323dcd26e76501b25dfd6a54
Reviewed-on: https://chromium-review.googlesource.com/1109039
Commit-Queue: Juan Antonio Navarro Pérez <perezju@chromium.org>
Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569215}

tools/perf/benchmarks/system_health_smoke_test.py

@@ -70,8 +70,6 @@ _DISABLED_TESTS = frozenset({
 
   # crbug.com/816482
   'benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_desktop/load:news:nytimes', # pylint: disable=line-too-long
-  # crbug.com/852888
-  'benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_mobile/load:news:nytimes', # pylint: disable=line-too-long
 })