Remove the replace directive and update x/tools.

For golang/go#67936

Change-Id: I87b28c57607c2ded4c2e6b47ce725d4365151795
Reviewed-on: https://go-review.googlesource.com/c/tools/+/593677
Reviewed-by: Alan Donovan <[email protected]>
Auto-Submit: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>