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 <[email protected]>
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>
Auto-Submit: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>