Fix regression in filter_avfilter
Fix regression in filter_avfilter

This filter used a workaround for the "height + 1" bug.
ae9b7de516627ab660756a8de1c58df5a8e38c54 removed the bug.
This commit removes the workaround so the filter works properly
again.

j-b-m/mlt,mltframework/mlt,mltframework/mlt,mltframework/mlt,mltframework/mlt,mltframework/mlt,j-b-m/mlt,mltframework/mlt,j-b-m/mlt,mltframework/mlt,j-b-m/mlt,j-b-m/mlt,j-b-m/mlt,mltframework/mlt,j-b-m/mlt,j-b-m/mlt,mltframework/mlt,mltframework/mlt,j-b-m/mlt,j-b-m/mlt