ffmpeg: do not build bottle with --enable-nonfree

faac, fdk-aac, and openssl are all distributed under GPL-incompatible
licenses; if ffmpeg is built with these libraries, it cannot legally
be redistributed.

faac has been replaced in the default build with libvo-aacenc, which
is not quite as good but is GPL3-licensed.
ffmpeg: update 2.4.4 bottle.