macosx: remove unneeded performSelectorOnMainThread
macosx: remove unneeded performSelectorOnMainThread

setActiveVideoPlayback is always called on the main thread nowadays..

(cherry picked from commit f737f942a5ace4cab4fb165b1eaeff8f036395fa)
Signed-off-by: Jean-Baptiste Kempf <7b85a41a628204b76aba4326273a3ccc74bd009a@videolan.org>

jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2