1.x: fix SafeSubscriber documentation regarding unsubscribe
1.x: fix SafeSubscriber documentation regarding unsubscribe

The documentation was wrong in two points: unsubscription doesn't call
onCompleted and unsubscription doesn't directly prevent delivery of
onXXX events since the implementation doesn't even check isUnsubscribed:
(it is the responsibility of the upstream to do that).
hzysoft/RxJava,stevegury/RxJava,zsxwing/RxJava,hzysoft/RxJava,simonbasle/RxJava,klemzy/RxJava,weikipeng/RxJava,jacek-rzrz/RxJava,tilal6991/RxJava,tilal6991/RxJava,davidmoten/RxJava,zsxwing/RxJava,jacek-rzrz/RxJava,simonbasle/RxJava,hyleung/RxJava,jacek-rzrz/RxJava,weikipeng/RxJava,stevegury/RxJava,tilal6991/RxJava,simonbasle/RxJava,hyleung/RxJava,klemzy/RxJava,weikipeng/RxJava,davidmoten/RxJava,hyleung/RxJava,stevegury/RxJava,zsxwing/RxJava,nurkiewicz/RxJava,davidmoten/RxJava,nurkiewicz/RxJava,nurkiewicz/RxJava,hzysoft/RxJava,klemzy/RxJava