Remove chaviw@google.com from libs/attestation/OWNERS

This suggested change is automatically generated based on group
memberships and affiliations.
If this change is unnecessary or in error, vote CR -1 and the bot
will abandon it. Vote CR +1/2 to approve this change.

See the owner's recent activity for context:
https://android-review.googlesource.com/q/chaviw@google.com

To report an issue, file a bug in the Infra>Codereview component.

Change-Id: I1a84685cccd68f53c097905ff425e6a084c39f4e