FFmpeg now requires that frames allocated with avcodec_alloc_frame are
freed with avcodec_free_frame.
(cherry picked from commit 77578d415f)
Conflicts:
modules/highgui/src/cap_ffmpeg_impl.hpp
The 'sysctl' syscall has been strongly deprecated on Linux for ages.
Currently, on old architectures it will spam syslog whenever used, and on
newer ones it's missing from the headers altogether. Opencv has migrated
away on Linux already, but #includes were left lingering. This commit
removes them on non-__APPLE__, unbreaking x32 (and probably others).
