Remove the replace directive and update x/tools.

For golang/go#67936

Change-Id: I15e14177f26afd0a7c1a86d4cf6c456b06614c01
Reviewed-on: https://go-review.googlesource.com/c/tools/+/593415
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Robert Findley <rfindley@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>