chore: remove stale_readers

The dedupe isn't needed for any test, including async-stale-read-multiple-no-double-run.

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

@@ -129,21 +129,6 @@ export class Batch {
 	 */
 	merged_into = null;
 
-	/**
-	 * @type {Set<Reaction> | null}
-	 */
-	#stale_readers = null;
-
-	/**
-	 * Reactions that, while running in an earlier batch, read a value that this batch holds
-	 * a newer version of, and that are therefore scheduled to re-run in this batch. Used to
-	 * avoid scheduling the same reaction multiple times when it reads more than one such value.
-	 * Lazily initialized for performance reasons.
-	 */
-	get stale_readers() {
-		return (this.#stale_readers ??= new Set());
-	}
-
 	/** @type {Batch | null} */
 	prev = null;
 

packages/svelte/src/internal/client/runtime.js

@@ -764,27 +764,18 @@ function get_batch_value(signal, first_time) {
 				(active_effect !== null && active_reaction === active_effect && (active_effect.f & REACTION_IS_UPDATING) !== 0) ||
 				(active_effect !== null && (active_effect.f & ASYNC) !== 0);
 
-			if (
+			if (reader !== null && reactive) {
-				reader !== null &&
-				reactive &&
-				// a reaction can read several stale values in one run — only schedule the re-run once
-				!batch.stale_readers.has(reader)
-			) {
-				batch.stale_readers.add(reader);
-
 				if (current.is_eager) {
 					// Reactions of eager effects with at least one non-eager effect (which we know is true here due to the stale_sources check above)
 					// need to rerun because they could do something like `$state.eager(count) !== count`.
 					if (reader.deps?.some((dep) => dep.f & EAGER_EFFECT)) {
 						batch.oncommit(() => {
-							batch.stale_readers.delete(reader);
 							Batch.ensure();
 							invalidate(reader, DIRTY);
 						});
 					}
 				} else {
 					queue_micro_task(() => {
-						batch.stale_readers.delete(reader);
 						const b = batch.activate();
 						invalidate(reader, MAYBE_DIRTY);
 						b.flush();