Disable multitab system_health smoke test.

7 minute execution time is causing flaky timeouts
in telemetry_perf_unittests.

TBR=sullivan@chromium.org,nednguyen@chromium.org

Bug: 893615
Change-Id: I73f3982453b418be59d6b7ed7067c1918c9d3d34
Reviewed-on: https://chromium-review.googlesource.com/c/1301959
Commit-Queue: John Budorick <jbudorick@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603132}

tools/perf/benchmarks/system_health_smoke_test.py

@@ -97,6 +97,9 @@ _DISABLED_TESTS = frozenset({
 
   # crbug.com/885320
   'system_health.memory_desktop/browse:search:google:2018',
+
+  # crbug.com/893615
+  'system_health.memory_desktop/multitab:misc:typical24:2018',
 })