ENG-5715: Clean up:
Remove dead code.
Delete RoadBlocks from RPQ
Delete unused method for DR
Delete unused field
Remove unused isHeartbeat argument
ENG-5715: Use the globally safe TXN ID to release transactions from
the AgreementSite's RestrictedPriorityQueue.  Ensures that synchronous
ZK writes only return when they've been witnessed by all nodes.
Merge pull request #1177 from VoltDB/eng5715

Eng5715