FIT performer is not validating errors

I noticed that the C++ FIT performer is only doing very basic error validation - whether it succeeds or fails.  FIT relies on performers validating the other fields of TransactionOperationFaileds to ensure correct operation - namely retry, rollback, and toRaise.  (ErrorClass no longer needs to validated.)

Please see the Java code for an example: https://github.com/couchbaselabs/transactions-fit-performer/blob/master/performers/java/txn-performer-java/src/main/java/com/couchbase/twoway/TwoWayTransactionShared.java#L369