chore: simplify flush_sync (#15346)

Author: Rich-Harris

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

@@ -858,19 +858,16 @@ export function flush_sync(fn) {
 	try {
 		infinite_loop_guard();
 
-		/** @type {Effect[]} */
-		const root_effects = [];
-
 		scheduler_mode = FLUSH_SYNC;
-		queued_root_effects = root_effects;
+		queued_root_effects = [];
 		is_micro_task_queued = false;
 
 		flush_queued_root_effects(previous_queued_root_effects);
 
 		var result = fn?.();
 
 		flush_tasks();
-		if (queued_root_effects.length > 0 || root_effects.length > 0) {
+		if (queued_root_effects.length > 0) {
 			flush_sync();
 		}