Remove duplicating code from blocking_observable.
Remove duplicating code from blocking_observable.

ReactiveX/RxCpp,Reactive-Extensions/RxCpp,ReactiveX/RxCpp,alexeymarkov/RxCpp,ReactiveX/RxCpp,alexeymarkov/RxCpp,Reactive-Extensions/RxCpp,alexeymarkov/RxCpp,Reactive-Extensions/RxCpp