cmd: update x/tools to pull in CL 315570

Since x/tools is now lazy, this removes a significant fraction of
otherwise-irrelevant dependencies from the go.sum file.

The remaining extraneous go.sum lines come from the dependency on
github.com/google/pprof. Since that module is outside of the Go
project proper, I do not plan to submit a PR to make it lazy until
after the Go 1.17 release.

For #36460
Updates #36905

Change-Id: I214492cf931fca797817124ecdcbccd4ebb7505b
Reviewed-on: https://go-review.googlesource.com/c/go/+/316452


Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Alexander Rakoczy <alex@golang.org>