ssh: shorten wait delay for external ssh binaries now that we are using go1.20

Now we are guaranteed to have go1.20 or later we can use the WaitDelay
flag when running external ssh binaries.

backend/sftp/ssh_external.go

@@ -10,6 +10,7 @@ import (
 	"io"
 	"os/exec"
 	"strings"
+	"time"
 
 	"github.com/rclone/rclone/fs"
 )
@@ -93,8 +94,7 @@ func (f *Fs) newSSHSessionExternal() *sshSessionExternal {
 	s.cmd = exec.CommandContext(ctx, ssh[0], ssh[1:]...)
 
 	// Allow the command a short time only to shut down
-	// FIXME enable when we get rid of go1.19
-	// s.cmd.WaitDelay = time.Second
+	s.cmd.WaitDelay = time.Second
 
 	return s
 }