Memory for auxillary_info was not freed after usage.

Leak can be reproduced with following commands:

Optionally, generate input video:
ffmpeg -f lavfi -i testsrc=duration=10:size=1280x720:rate=30 input.mp4

Run ffmpeg with valgrind:
valgrind --leak-check=full --show-leak-kinds=all \
ffmpeg -y -i input.mp4 -vcodec copy -acodec copy \
-encryption_scheme cenc-aes-ctr \
-encryption_key 00000000000000000000000000000000 \
-encryption_kid 00000000000000000000000000000000 \
ffmpeg_encrypted.mp4

For test video which has duration of 10 sec, leak is 4 Kb.
For 100 sec video, leak will be 33 Kb. Most likely,
leaked memory will grow linearly to the number of input frames.
Signed-off-by: Vadym Bezdushnyi <vadim.bezdush@gmail.com>
Signed-off-by: Marton Balint <cus@passwd.hu>