### _Why are the changes needed?_
- DISCLAIMER file on top-level folder of project was already removed after graduation in (https://github.com/apache/kyuubi/issues/4020)
- fix build/dist for `cp` non-existed DISCLAIMER file
- remove DISCLAIMER file reference in dev/dist script, doc
### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible
- [ ] Add screenshots for manual tests if appropriate
- [x] [Run test](https://kyuubi.apache.org/docs/latest/develop_tools/testing.html#running-tests) locally before make a pull request
Closes#4086 from bowenliang123/desclaimer-ref.
Closes#4086
18be7489 [liangbowen] remove DISCLAIMER file reference in dev/dist script, doc, docker , labeler.yml
Authored-by: liangbowen <liangbowen@gf.com.cn>
Signed-off-by: Cheng Pan <chengpan@apache.org>
090e5bf4f2