all: cleanup unused code, part 1 (#10661)

Run `staticcheck` with `U1000` to find unused code. This cleans up about
a half of it. I'll do the other half separately to keep PRs manageable.

Updates #cleanup

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

tstest/integration/vms/vms_steps_test.go

@@ -19,8 +19,6 @@ import (
 	"golang.org/x/crypto/ssh"
 )
 
-const timeout = 15 * time.Second
-
 func retry(t *testing.T, fn func() error) {
 	t.Helper()
 	const tries = 3