[Improve][Connector-v2] Remove useless code and add changelog doc for paimon sink

[dailai]

Purpose of this pull request

1. Remove useless code and add changelog doc for paimon sink
2. remove br from doris.md to fix ci error

Does this PR introduce any user-facing change?

How was this patch tested?

Check list

• If any new Jar binary package adding in your PR, please add License Notice according
  New License Guide
• If necessary, please update the documentation to describe the new feature. https://github.com/apache/seatunnel/tree/dev/docs
• If you are contributing the connector code, please check that the following files are updated:
  1. Update plugin-mapping.properties and add new connector information in it
  2. Update the pom file of seatunnel-dist
  3. Add ci label in label-scope-conf
  4. Add e2e testcase in seatunnel-e2e
  5. Update connector plugin_config
• Update the release-note.

[wuchunfu]

LGTM, Waiting for CI to pass, thanks @dailai