remove native scan query legacy mode

[clintropolis]

Description

The native scan query was moved from a contrib extension into core in Druid 0.11 in #4751, which introduced a 'legacy' option to maintain backwards compatibility with the extension, which used a non-standard time column name and always included this timestamp in the results.

I think sufficient time has passed to allow us to remove this parameter to help simplify code a bit.

Release note

The native scan query 'legacy' mode has been removed, which was introduced in Druid 0.11 to maintain compatibility during an upgrade from older versions of Druid where the scan query was part of a 'contrib' extension.

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This PR has:

• [x] been self-reviewed.
• [x] added documentation for new or modified features or behaviors.
• [x] a release note entry in the PR description.
• [ ] been tested in a test Druid cluster.

[clintropolis]

CI failures are related to coverage, which I guess means this stuff wasn't well covered in the first place since I am only removing stuff in this PR. Can look into maybe adding some more tests to get it happy, but also doesn't really feel like a blocker

[kgyrtkirk]

oh...covereage change issues have prevented further tests from being run... or somehow re-organize the maven target order... I think there should be a way to disable that; this is a perfect example - there were issues arising from that earlier

In this case I think that doesn't really apply as these jobs were running with -pl processing already - but coverage issues are evil when they happen in the other modules splits