kubernetes: Remove dependency on github.com/pkg/errors

Why is this needed?

The functionality that the package provides is already present in golang’s builtin errors (using %w in fmt.Errof) and the github repo is now read-only.

/kind cleanup /priority backlog /good-first-issue

Notes to people that want to collaborate

Avoid creating a single PR for the entire repo. Create multiple PRs, each targeting a specific SIG.

Do not submit PRs for cmd/kubeadm