fix(#58): remove broken getElementById('contactForm') stub

The JS had a dangling document.getElementById('contactForm') call that
did nothing - no event handler attached, no return value used.

Form handling is entirely server-side (PHP POST → redirect to #form-result).
No JS form intervention needed.

Closes #58

public/js/haus-schleusingen.js

@@ -176,8 +176,7 @@ document.addEventListener("DOMContentLoaded", function () {
   });
 
   // Form submit is handled server-side by PHP – no JS intervention needed.
-  // Form submit – opens email client with pre-filled mailto: link
-  document.getElementById("contactForm")
+  // Success feedback is shown via #form-result after server redirect.
   });
 });