Remove delete user in OrderSubscriber on filled. (drift-labs#1245)

This can be problematic if account updates are received out of order, or `tryUpdateUserAccount` is invoked out of order.
If an account update for a slot `t-1` is received for an order filled at slot `t`, then the `OrderSubscriber` will
erroneously report the open order.

sdk/src/orderSubscriber/OrderSubscriber.ts

@@ -209,11 +209,8 @@ export class OrderSubscriber {
 					dataType
 				);
 			}
-			if (userAccount.hasOpenOrder) {
-				this.usersAccounts.set(key, { slot, userAccount });
-			} else {
-				this.usersAccounts.delete(key);
-			}
+
+			this.usersAccounts.set(key, { slot, userAccount });
 		}
 	}