timezone: only set the placeholder and not the value automatically because it is confusing

Signed-off-by: Simon L. <szaimen@e.mail.de>

php/public/timezone.js

@@ -2,6 +2,6 @@ document.addEventListener("DOMContentLoaded", function(event) {
     // timezone
     let timezone = document.getElementById("timezone");
     if (timezone) {
-        timezone.value = Intl.DateTimeFormat().resolvedOptions().timeZone
+        timezone.placeholder = Intl.DateTimeFormat().resolvedOptions().timeZone
     }
 });