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/test/banner_test.go

@@ -8,7 +8,6 @@ package test
 
 import (
 	"testing"
-
 )
 
 func TestBannerCallbackAgainstOpenSSH(t *testing.T) {