Merge EvictionListener.preEvict() and postEvict() into one listener method.

EvictionListener.preEvict() is of dubious value (and actually the legacy of JBoss Cache) because a user cannot affect the behavior of eviction at all and a user can get notified on eviction via the postEvict() listener method. I'd like to propose to change EvictionListener like this:

public interface EvictionListener<K, V>

{ void onEntryEviction(K key, V value); }