Remove the replace directive and update x/tools.

For golang/go#66730

Change-Id: Icb7444a1ebeeeb8e95cc6639c4e6038a17a56735
Reviewed-on: https://go-review.googlesource.com/c/tools/+/577656
Reviewed-by: Alan Donovan <adonovan@google.com>
Auto-Submit: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>