Remove "Cannot create allocations for active order" Exception

[ReichPhilipp]

Is your feature request related to a problem? Please describe.
If you want to change the allocation strategy in this way:

shouldAllocateStock(ctx: RequestContext, fromState: OrderState, toState: OrderState, order: Order): boolean | Promise<boolean> {
    // custom
    if (fromState === "AddingItems" && toState === "ArrangingPayment") {
      return true;
    }
    // default
    return fromState === "ArrangingPayment" && (toState === "PaymentAuthorized" || toState === "PaymentSettled");
  }
}

The vendure core stock-movement.service.ts (Line 140f) will raise an error, because the order is not inactive. We can setup only inactive orders. We shortly discussed this behaviour in the discord channel.

Looks like that this is a relic, from stock movement refractoring.

Describe the solution you'd like
Remove this check?