Legacy DTXN purge: Delete RecoveringSinglePartitionTxnState, which was
apparently not even used by legacy DTXN.
Legacy DTXN purge: Remove unused-by-IV2 SinglePartitionTxnState
For ENG-4513, fix what may be a longstanding race between leader elector and shutdown it tests.
Legacy DTXN purge: Remove unused-by-IV2 ReplayedTxnState and junit
test.
Legacy DTXN purge: Remove unused SimpleDtxnInitiator.  All of its
threads were hacked off in an elastic-motivated commit set earlier.
Legacy DTXN purge: Remove unused-by-IV2 DtxnInitiatorMailbox and junit
test.
Legacy DTXN purge: Remove unused-by-IV2 ExecutorTxnIdSafetyState.
Legacy DTXN purge: Remove unused-by-IV2 WorkUnit.java
Legacy DTXN purge: Remove SiteTransactionConnection.
- Remove legacy constructor for TransactionState
Legacy DTXN purge: Remove unused-in-IV2 InFlightTxnState and junit
test.
Legacy DTXN purge:  TransactionState and its remaining subclasses no
longer require or implement the handleSiteFaults() method.
schemachange app: add duration and change iteration count
Eliminate another unused TransactionState method.
Remove another spurious TransactionState method.
Remove two more unused TransactionState methods.  Remove unused
RejoinState machinery.
Remove TransactionState.isBlocked()
Remove TransactionState.hasTransactionalWork()
Get rid of TransactionState.doWork()
Get rid of TransactionState.setResumeProcedure()
Get rid of TransactionState.processRemoteWorkResponse()