ReplicationCoordinator::isMasterForReportingPurposes() is only used in appendReplicationInfo() and for SNMP (in IsMasterCallback). Since we've removed master and slave, we can get rid of the dead code. SNMP will need to get the result in other ways.

redbeard0531 found that ReplicationCoordinator::isMasterForReportingPurposes() reports a wrong result if the node is in catchup mode or drain mode.