Revert "Add OWNERS for templates"

This reverts commit a3e9a3f (#1279).

Using filters for approvers and reviewers is the long-term goal, but
the approve plugin can't handle this yet [1,2].

[1]: kubernetes/test-infra#7690
[2]: https://github.com/kubernetes/community/blame/19dc4bed5b05c23a69e631f96573f8ed2e0774cb/contributors/guide/owners.md#L86-L87