Rewrite OperationObserveFromAndroidComponent to OperatorObserveFromAndro...

This PR did the following things:
* Rewrite `OperationObserveFromAndroidComponent` to `OperatorObserveAndroidComponent`.
* Call `unsubscribe` at once if the current thread is the UI thread.
* Remove `itUnsubscribesFromTheSourceSequence` since it's meaningless in the new design.