Re-enable some tests in system_health_smoke_test.

A bug in catapult caused these tests to fail. That bug was fixed:
https://chromium-review.googlesource.com/c/catapult/+/730856

Bug: chromium:778169, chromium:778095, chromium:776608
Change-Id: Ieed45163b23b3a604efee248e99c2ea14661e744
Reviewed-on: https://chromium-review.googlesource.com/742393Reviewed-by: Ned Nguyen <nednguyen@google.com>
Commit-Queue: Ben Hayden <benjhayden@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512712}

tools/perf/benchmarks/system_health_smoke_test.py

@@ -66,15 +66,6 @@ _DISABLED_TESTS = frozenset({
 
   # crbug.com/725386
   'benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_desktop.browse:social:twitter', # pylint: disable=line-too-long
-
-  # crbug.com/778095
-  'benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_desktop.multitab:misc:typical24',  # pylint: disable=line-too-long
-
-  # https://crbug.com/778169
-  'benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_desktop.browse:news:flipboard',  # pylint: disable=line-too-long
-
-  # https://crbug.com/778169
-  'benchmarks.system_health_smoke_test.SystemHealthBenchmarkSmokeTest.system_health.memory_desktop.load:games:alphabetty',  # pylint: disable=line-too-long
 })