cmd/go.sum: remove untidy checksums

I missed the 'go mod tidy' step in CL 316751 because I forgot to run
the cmd/internal/moddeps test in long mode. 😞

Updates #45932

Change-Id: Ic3f9b303ad5798ecd8cb044d4b8c766aa820bf69
Reviewed-on: https://go-review.googlesource.com/c/go/+/317129


Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>