The batch segment sampling performs significantly better than the older method
of sampling if there are a large number of used segments. It also avoids duplicates.
Changes:
- Make batch segment sampling the default
- Deprecate the property `useBatchedSegmentSampler`
- Remove unused coordinator config `druid.coordinator.loadqueuepeon.repeatDelay`
- Cleanup `KillUnusedSegments`
- Simplify `KillUnusedSegmentsTest`, add better tests, remove redundant tests