Remove crossdoc variant from nested VT test
It's a very flaky test, and the scenario is already tested in the
mpa-serialization suite.
Bug: 358842552
Change-Id: I72c4b24f44b4b9c136f9bce0e1b4887e12346528
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5850138
Reviewed-by: Vladimir Levin vmpstr@chromium.org
Commit-Queue: Noam Rosenthal nrosenthal@chromium.org
Cr-Commit-Position: refs/heads/main@{#1355063}