Convert video in a single ffmpeg call

[Logerfo]

I'm not sure how, but I think it's possible to merge the following calls to a single one, which can possibly be faster:

surdobot/src/chalicelib/file_utils.py

Lines 49 to 50 in 0827aa8

	subprocess.Popen(['ffmpeg', '-y', '-i', MP4_FILE_NAME, '-vn', '-acodec', 'copy', AAC_FILE_NAME]).wait()
	subprocess.Popen(['ffmpeg', '-y', '-i', AAC_FILE_NAME, '-map', '0:a:0', '-b:a', '41k', MP3_FILE_NAME]).wait()