Remove RecoveryAwareGlobalTransaction

Currently there exists both the GlobalTransaction and RecoveryAwareGlobalTransaction which implements RecoverableTransactionIdentifier. If we add the `Xid` and `internalId` fields to GlobalTransaction, the latter are redundant. We should remove theses classes as it simplifies the ProtoStream marshalling code required by commands such as PrepareCommand as they don't have to handle the polymorphism.