0330: use `data:,` for toolkit.telemetry.server

see https://github.com/ghacksuserjs/ghacks-user.js/commit/3d5276484a5a278b9881867852c9ce67be7e1494#commitcomment-27760142

user.js

@@ -173,7 +173,7 @@ user_pref("extensions.webservice.discoverURL", "");
  * [2] https://medium.com/georg-fritzsche/data-preference-changes-in-firefox-58-2d5df9c428b5 ***/
 user_pref("toolkit.telemetry.unified", false);
 user_pref("toolkit.telemetry.enabled", false); // see [NOTE] above FF58+
-user_pref("toolkit.telemetry.server", "");
+user_pref("toolkit.telemetry.server", "data:");
 user_pref("toolkit.telemetry.archive.enabled", false);
 user_pref("toolkit.telemetry.cachedClientID", "");
 user_pref("toolkit.telemetry.newProfilePing.enabled", false); // (FF55+)