Revert "Re-enable TwoClientDictionarySyncTest.Sanity_E2ETest test"

This reverts commit ad88c6d1.

Reason for revert: Still fails on bot. This is weird. I've used mb tool to launch the job and it can pass on bot. Tried several times. But on CI bot it still fails.

Original change's description:
> Re-enable TwoClientDictionarySyncTest.Sanity_E2ETest test
>
> Tested the test can pass on bot.
>
> Bug: 1068415
> Change-Id: I3a94ededc3969f3cdef01865ced46c2ad4d0e300
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2157783
> Reviewed-by: Ian Struiksma <ianstruiksma@google.com>
> Commit-Queue: Sven Zheng <svenzheng@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#761327}

TBR=svenzheng@chromium.org,ianstruiksma@google.com

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

TBR: ianstruiksma@chromium.org
Bug: 1068415
Change-Id: I317e83cad99f0573b4e1abe1e6b74a6092eebf16
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2163249
Commit-Queue: Sven Zheng <svenzheng@chromium.org>
Reviewed-by: Ian Struiksma <ianstruiksma@google.com>
Reviewed-by: Sven Zheng <svenzheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#761985}

testing/buildbot/filters/e2e.sync_integration_tests.filter

 # This is the filter file for sync e2e tests.
 
+# TODO(crbug.com/1068415): Disabled because it's flaky.
+-TwoClientDictionarySyncTest.Sanity_E2ETest