Remove the replace directive and update x/tools.

For golang/go#63220

Change-Id: Iea9521860c8b8c256dccf38ea3e45425e97a38ae
Reviewed-on: https://go-review.googlesource.com/c/tools/+/537375
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
Auto-Submit: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>