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 <[email protected]>
Reviewed-by: Peter Weinberger <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>