[Documentation] v4 Docs remove() references tracks instead of indices

[uzegonemad]

The docs currently state that the remove() method expects a Track(s). It actually expects an index/indices, and passing tracks will crash the app (at least on iOS).

Note: I haven't confirmed if any other methods in the docs are also outdated.

[krestaino]

I can confirm the same on Android. I didn't know if it was a bug or simply the docs needed to be updated, but since it's like this on iOS and this looks like code for Android, I'm assuming the docs just need to be updated.