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 <[email protected]>
Auto-Submit: Robert Findley <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>