Remove CODEOWNERS after auto reviewer assign is added (sonic-net#21862)

What is the motivation for this PR?
This repo has enabled auto code reviewer assign according to the git history. The .github/CODEOWNERS file is now outdated and not necessary.

Background of auto code reviewer assign
It is tedious to manually maintain the CODEOWNERS file. @nikamirrr from Nvidia contributed auto code reviewer assign workflow: https://github.com/sonic-net/sonic-mgmt/actions/workflows/code-reviewer-tagging.yml

This automation automatically check git history of files updated by PR. Find out the previous contributors of the touched files and assign them as reviewer of the PR.

This automation has 2 major benefits:

No need to manually maintain the CODEOWNERS file.
Automatically find the most appropriate owners/reviewers. Not able to find appropriate owner of code has been a pain point of community for quite some time.
For details, please refer to https://github.com/sonic-net/sonic-pipelines/tree/main/scripts/code-owners

How did you do it?
This change deleted this .github/CODEOWNERS file.

Signed-off-by: Xin Wang <xiwang5@microsoft.com>
Signed-off-by: Saravanan Sellappa <saravanan@nexthop.ai>

Author: wangxin