Fix black screen: remove MutationObserver freeze

src/display/css_html_js.py

@@ -119,16 +119,6 @@ def eval_countdown_head_js() -> str:
   function boot() {
     tick();
     startInterval();
-    if (window.__tsfmEvalCountdownObserver) return;
-    window.__tsfmEvalCountdownObserver = new MutationObserver(function () {
-      if (document.getElementById("tsfm-eval-countdown")) {
-        tick();
-      }
-    });
-    window.__tsfmEvalCountdownObserver.observe(document.body, {
-      childList: true,
-      subtree: true,
-    });
   }
 
   if (document.readyState === "loading") {