sys.segment's is_realtime flag once set, is never unset #8142

Affected Version

0.15

Description

In the system schema's sys.segments table, the is_realtime flag is set when a segment is added via segmentAdded callback in DruidSchema. But it's not unset when a segment is dropped from realtime task and published on historicals. So when serverSegmentRemoved is called, the is_realtime flag should be unset.
This was reported here https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!msg/druid-user/t-215-pIJO4/yG9Y5VRLDwAJ