Revert "Disable flaky system_health.memory_desktop/browse_accessibility:media:youtube"

This reverts commit 02b03541.

Reason for revert: Test no longer appears to fail.

Original change's description:
> Disable flaky system_health.memory_desktop/browse_accessibility:media:youtube
>
> TBR=perezju@chromium.org
>
> Bug: 983326
> Change-Id: I22be996f9054935f378a05b95f7f7924a9c5f63b
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1699097
> Reviewed-by: danakj <danakj@chromium.org>
> Commit-Queue: danakj <danakj@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#677130}

TBR=crouleau@chromium.org

Bug: 983326
Change-Id: If9cb5e9a1d674e49709edbbee4dd2ceafe5bb21b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1871998Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Commit-Queue: Juan Antonio Navarro Pérez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708139}

tools/perf/benchmarks/system_health_smoke_test.py

@@ -36,9 +36,6 @@ def GetSystemHealthBenchmarksToSmokeTest():
 
 
 _DISABLED_TESTS = frozenset({
-  # crbug.com/983326 - flaky.
-  'system_health.memory_desktop/browse_accessibility:media:youtube',
-
   # crbug.com/878390 - These stories are already covered by their 2018 versions
   # and will later be removed.
   'system_health.memory_mobile/browse:tech:discourse_infinite_scroll',