Switch dart2js nnbd bot: use a sdk-built configuration with no assertions
Switch dart2js nnbd bot: use a sdk-built configuration with no assertions

This is a temporary measure to help run the bots faster (the hostasserts
configuration seems to be timing out periodically)

See also https://github.com/dart-lang/sdk/issues/40521

Change-Id: Iba06626388124c146fbde8e78f3edc0a62f089f0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/134885
Reviewed-by: Mayank Patke <e0355b78204b67a55a952941c68c8f1b40235938@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk