Here is the reason why the button is there, and the way to hide it :
Video Player unexpectedly shows Alternate Track button for Subtitles and Captions
The source material will have to include: CLOSED-CAPTIONS=NONE on the EXT-X-STREAM-INF tag to remove the Button.
Edit :
I've been searching on "how to insert HTTP headers for a URL" and found a few interesting results. First, if you really want to insert HTTP headers to your URL, the following might do the job :
NSMutableURLRequest* request = [[NSMutableURLRequest alloc] initWithURL:url];
[request setValue:@"NONE" forHTTPHeaderField:@"CLOSED-CAPTIONS"];
If it's not what you're searching for, the solution suggested here could make the job :
I think setting a cookie might solve your problem. Please look into the documentation for NSHTTPCookie and NSHTTPCookieStorage.
If it's still not working, take a look at this related question.
Finally, if all those steps didn't help, implement your own control bar thanks to this tutorial.