sweet: disable gvisor benchmark

This reverts CL 390955.

Reason for revert: benchmark is still failing on longtest builders.

Updates golang/go#51445.

Change-Id: I35a057933231e89e5b56810ff39c73f3702fd383
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/391194
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>