Remove legacy RestrictedPriorityQueue (not the one used by
AgreementSite).
With RPQ gone, RPQInterface is also unnecessary.
In IV2, SiteMailbox no longer needs to know about the command log.
Also, clean up some stale imports.
Get rid of unused logHeartbeat method on CommandLog.
Hey, look, we don't log old-style legacy faults anymore, either.
IV2 command logging doesn't have or care about the fault sequence
number.
Merge pull request #439 from VoltDB/rpqpurge

Remove legacy command logging code