ffmpeg: remove libavdevice from the libffmpeg-mini variant

As libffmpeg-mini is intended for DLNA purposes, it needs only
to identify media, not interact with input or output devices.

Signed-off-by: Ian Leonard <antonlacon@gmail.com>
ffmpeg: remember to adjust InstallDev too

Finish adjustment for libavdevice with libffmpeg-mini

Signed-off-by: Ian Leonard <antonlacon@gmail.com>