Shrinker for a call sequence failure.
Iterates sequence call sequence top down and removes calls one by one.
If the failure is still reproducible with removed call then moves to the next one.
If the failure is not reproducible then restore removed call and moves to next one.
Shrinks a call sequence to the shortest sequence that still produces the target optimization
value. This is specifically for optimization mode where we want to find the minimal sequence
that achieves the maximum value.