Remove the replace directive and update x/tools.

Also run `go mod tidy -compat=1.18`, which actually removes some sum
entries now that we no longer require 1.16 compatibility.

For golang/go#63220

Change-Id: I6b02a965275e7fc9bd18279831141d5660842c53
Reviewed-on: https://go-review.googlesource.com/c/tools/+/530437
Reviewed-by: Peter Weinberger <[email protected]>
Auto-Submit: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>