Remove commit() method Firehose

[jihoonson]

Description

commit() method was implemented only by the ancient kafka firehose which was removed in #8020.

---

This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added or updated version, license, or notice information in licenses.yaml
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths.
• added integration tests.
• been tested in a test Druid cluster.

---

This change is 

[lgtm-com]

This pull request fixes 2 alerts when merging 6038515 into 89ce638 - view on LGTM.com

fixed alerts:

• 2 for Dereferenced variable may be null

[ccaominh]

LGTM 👍

[clintropolis]

👍

[clintropolis]

It seems like a smell that this class still exists and only has this nil supplier, and maybe can be removed entirely. But I'm ok if we continue clean-up in the future since this looks a bit more invasive to dump than just removing commit from the Firehose.

[fjy]

Agree that we should remove the nil supplier. A follow up PR is fine as long as we remember to do it...