Function remove_final_keys 

pub fn remove_final_keys(clip: &mut Clip) -> usize

Remove one final key from every nonempty track and shorten the clip to the latest remaining key.

This is useful for converting a duplicate-endpoint loop to an open loop. Empty tracks are removed. If every track becomes empty, the duration is zero. Cubic-spline tangent/value/tangent triplets are removed together. Returns the number of keys removed.