clutter-damage-history: Limit history to 4 entries

Having 4 entries actually supports 5 unique buffers used by the driver but realistically we never see more than triple buffers (max buffer age 2) in the wild.

Reducing the history length reduces the number of wasted regions that will never be used again before they are destroyed. So at its peak (during icon spring animations) the history now only consumes ~30KB instead of ~90KB.