Revert "macosx: fixed compilation warning and potential, runtime exception"

This reverts commit 55e3f94302a29e9ee76532c290c1134af5f0213e and fixes it the right way. I'm honestly not sure what's going on in that commit -- it silences the compiler warning not by actually fixing the problem (which is that the method isn't declared in the interface) but just by not making the method call visible to the compiler! It also completely breaks the feature, by moving things onto the main thread that can't be there, causing a deadlock, as specifically noted in the comment right above this code.

In any event, it's easy enough to revert and add to the interface properly, silencing the compiler warning and unbreaking this extension feature.

Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>