all: run gofmt -s on source code

Per the description, the "-s" file issues slight simplifications to
the source code.

Change-Id: I77395d763f5eafb48653902dcedfa56b150b2d67
Reviewed-on: https://go-review.googlesource.com/80138
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

ssh/certs.go

@@ -343,7 +343,7 @@ func (c *CertChecker) CheckCert(principal string, cert *Certificate) error {
 		return fmt.Errorf("ssh: certicate serial %d revoked", cert.Serial)
 	}
 
-	for opt, _ := range cert.CriticalOptions {
+	for opt := range cert.CriticalOptions {
 		// sourceAddressCriticalOption will be enforced by
 		// serverAuthenticate
 		if opt == sourceAddressCriticalOption {