fix: remove sanposhiho from CODEOWNERS

[sanposhiho]

What this PR does / why we need it:

This PR removes me from the CODEOWNERS list.
My entire OSS work time is very limited (since it's just a hobby, unpaid work for fun), and the more responsibilities I've got in Kubernetes project, the less time I can spend on other projects, including Tortoise here.
I LOVE the idea here, and I still strongly believe this idea could change the whole resource requirement concept in Kubernetes. So, I was hoping I could continue spending more time on this project after leaving Mercari, but it didn't come true, unfortunately.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

[AVSBharadwaj]

Heyy sanposhiho,
I understand the constraints on your time. Thank you for giving birth to Tortoise and also nurturing it all the while. Your vision for this project has been valuable. Removing you from CODEOWNERS makes sense given your current commitments. Approved!
Would love to see you around though !!