chore: remove unused class property (#18307)

remnant of blocker approach

packages/svelte/src/internal/client/reactivity/batch.js

@@ -127,13 +127,6 @@ export class Batch {
 	 */
 	previous = new Map();
 
-	/**
-	 * Async effects which this batch doesn't take into account anymore when calculating blockers,
-	 * as it has a value for it already.
-	 * @type {Set<Effect>}
-	 */
-	unblocked = new Set();
-
 	/**
 	 * When the batch is committed (and the DOM is updated), we need to remove old branches
 	 * and append new ones by calling the functions added inside (if/each/key/etc) blocks