ENG-5715: Clean up:
Remove dead code.
Delete RoadBlocks from RPQ
Delete unused method for DR
Delete unused field
Remove unused isHeartbeat argument
(cherry picked from commit d1887bc7a742a9c12b0a62815aabd60e86c25264)
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.
(cherry picked from commit 208388da0a6a4dcf4f3f75dd1cc77f9f6c1a6dab)