Backout RevObject's object-identity based equals implementation

Backout RevObject's  object-identity based equals implementation

This restores the transitivity and symmetry properties of the equals
methods on the AnyObjectId type hierarchy as defined in [1].
Following [2] we declare these equals methods final to ensure that
semantics of equals are consistent across AnyObjectId's type hierarchy.

[1] http://download-llnw.oracle.com/javase/6/docs/api/java/lang/Object.html#equals(java.lang.Object)
[2] http://www.angelikalanger.com/Articles/JavaSolutions/SecretsOfEquals/Equals.html

Bug: 321502
Change-Id: Ibace21fa268c4aa15da6c65d42eb705ab1aa24b3
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>