vout: remove unnecessary lock around the picture FIFO
vout: remove unnecessary lock around the picture FIFO

The picture FIFO has a lock internally to protect its internal state
while picture references protect the pictures.

There is no need to protect the FIFO usage with the picture lock.
At this point, the picture lock is only protected the decoder pool.

krichter722/vlc,shyamalschandra/vlc,vlc-mirror/vlc,krichter722/vlc,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,krichter722/vlc,shyamalschandra/vlc,vlc-mirror/vlc,krichter722/vlc,xkfz007/vlc,vlc-mirror/vlc,shyamalschandra/vlc,vlc-mirror/vlc,xkfz007/vlc,xkfz007/vlc,krichter722/vlc,shyamalschandra/vlc,shyamalschandra/vlc,vlc-mirror/vlc,krichter722/vlc,shyamalschandra/vlc,krichter722/vlc,xkfz007/vlc,xkfz007/vlc,vlc-mirror/vlc,shyamalschandra/vlc