Remove the replace directive and update x/tools.

For golang/go#63756

Change-Id: I5e24914c2032ff21d781453ebed1be04215ac6f2
Reviewed-on: https://go-review.googlesource.com/c/tools/+/537880
Auto-Submit: Robert Findley <rfindley@google.com>
Reviewed-by: Peter Weinberger <pjw@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>