Changed coroutine delays to not allocate every time

DOTS_Pong/Assets/Scripts/GameManager.cs

 	Entity ballEntityPrefab;
 	EntityManager manager;
 
+	WaitForSeconds oneSecond;
+	WaitForSeconds delay;
+
 	private void Awake()
 	{
 		if (main != null && main != this)
 		main = this;
 		playerScores = new int[2];
 
-		manager = World.Active.EntityManager;
+		manager = World.DefaultGameObjectInjectionWorld.EntityManager;
+		oneSecond = new WaitForSeconds(1f);
+		delay = new WaitForSeconds(respawnDelay);
+
 		StartCoroutine(CountdownAndSpawnBall());
 	}
 
 	IEnumerator CountdownAndSpawnBall()
 	{
 		mainText.text = "Get Ready";
-		yield return new WaitForSeconds(respawnDelay);
+		yield return delay;
-		WaitForSeconds delay = new WaitForSeconds(1f);
-		yield return delay;
+		yield return oneSecond;
-
-		yield return delay;
+		yield return oneSecond;
-
-		yield return delay;
+		yield return oneSecond;
 
 		mainText.text = "";