sweet/common: remove redundant word in comment

Change-Id: I2b18c42e9799943f559142f54b5d6d51ec8aafe0
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/690795
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>