Disable sb3 optimization again

Mangling variable IDs can cause unexpected behaviors in the backpack, for example

src/serialization/sb3.js

@@ -526,7 +526,7 @@ const serializeMonitors = function (monitors, runtime) {
  * @param {string=} targetId Optional target id if serializing only a single target
  * @return {object} Serialized runtime instance.
  */
-const serialize = function (runtime, targetId, {allowOptimization = true} = {}) {
+const serialize = function (runtime, targetId, {allowOptimization = false} = {}) {
     // Fetch targets
     const obj = Object.create(null);
     // Create extension set to hold extension ids found while serializing targets