Switch GVL updates to manual synchronization

src/background.js

@@ -22,7 +22,7 @@ browser.webRequest.onBeforeRequest.addListener(
   { urls: ["<all_urls>"] }
 );
 
-void runStartupGvlAutoUpdateCheck();
+console.info("GVL auto update disabled; use manual sync");
 
 async function handleVendorGetMessage(message, sender) {
   if (!message) {