ApplyDeltaCommand.getAffectedKeys() and ApplyDeltaCommand.getKey() do not return the expected key

These methods should return the map key but null is returned instead because the super constructor is not invoked correctly.

See discussion on infinispan dev list here: http://markmail.org/message/dkoughqngztmxvuy

This class could also be simplified a bit by removing the field deltaAwareValueKey which duplicates the key field of the base class.

Also since keys are non-null (asserted by constructor) the equals() and hashCode() methods can be simplified by removing the null checks.