Remove the replace directive and update x/tools.

For golang/go#68244

Change-Id: I198a04a24bb96e0b58558440a9541d9cb8648e62
Reviewed-on: https://go-review.googlesource.com/c/tools/+/595955
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>