cmd/go: go clean should not accept flags like -modcache with packages

cmd/go: go clean should not accept flags like -modcache with packages

For #53725

Change-Id: I99a85b437d5f918dba74c4eccefcf8087193646a
Reviewed-on: https://go-review.googlesource.com/c/go/+/425874
Run-TryBot: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>