LeaderElector: Remove unneeded child watcher
LeaderElector: Remove unneeded child watcher

When the method noticedTopologyChange() was removed from LeaderNoticeHandler
the child watcher become unused but was left in the LeaderElector. Remove the
child watcher and associated members.

VoltDB/voltdb,VoltDB/voltdb,VoltDB/voltdb,VoltDB/voltdb,VoltDB/voltdb,VoltDB/voltdb,VoltDB/voltdb