Delay delays cancelled stream completion

[Cy-4AH]

https://github.com/ReactiveCocoa/ReactiveObjC/blob/1af6617f007cae727dce48d2031cc1e66d06f04a/ReactiveObjC/RACSignal%2BOperations.m#L215

I understand that current code prevents earlier stream completion, but it's not needed if subscription is cancelled. Also completion is delayed but it can be called just right after the last next.