Cleanup OWNERS (#44)

Currently, pull requests get auto-assigned `reviewers` (and `approvers`) by the @kserve-oss-bot
However, many of the reviewers and approvers are no longer active. When inactive reviewers are auto-assigned, then active contributors who could actually help with reviews are not notified about new PRs.

Similarly, the @kserve-oss-bot adds a message to PRs about who is allowed to approve PRs, which often points to inactive contributors.

- Following [Kubernetes guidance](https://www.kubernetes.dev/docs/guide/owners/#cleanup), moving inactive `approvers` under `emeritus_approvers`, removing inactive contributors from list of `reviewers`
- Adding currently active contributors to the list of `reviewers`
- Removing `reviewers` who are no longer working on the project

An updated OWNERS file. Auto-assigned reviewers are currently active.

- [ ] kserve/modelmesh#89
- [ ] kserve#44
- [ ] kserve/modelmesh-serving#354

Signed-off-by: Christian Kadner <[email protected]>

OWNERS

@@ -11,4 +11,3 @@ reviewers:
   - Jooho
   - VedantMahabaleshwarkar
   - Xaenalt
-