metropolis/node/kubernetes/reconciler: remove redundant nil check

Change-Id: I0ebd2d8d815a964fa854e86868a4870b754ea548
Reviewed-on: https://review.monogon.dev/c/monogon/+/3015
Reviewed-by: Serge Bazanski <serge@monogon.tech>
Vouch-Run-CI: Tim Windelschmidt <tim@monogon.tech>
Tested-by: Jenkins CI
diff --git a/metropolis/node/kubernetes/reconciler/reconciler.go b/metropolis/node/kubernetes/reconciler/reconciler.go
index 13b71cf..f2c3838 100644
--- a/metropolis/node/kubernetes/reconciler/reconciler.go
+++ b/metropolis/node/kubernetes/reconciler/reconciler.go
@@ -71,10 +71,8 @@
 	l := map[string]string{
 		BuiltinLabelKey: BuiltinLabelValue,
 	}
-	if extra != nil {
-		for k, v := range extra {
-			l[k] = v
-		}
+	for k, v := range extra {
+		l[k] = v
 	}
 	return l
 }