remove upstream CI/CD workflows inherited from minio/minio

We maintain our own release pipeline (release.yml, test-release.yml)
and have no use for the upstream test/lint/integration workflows.
They reference infrastructure and secrets we don't have, and the
PR-triggered jobs never fire since we don't take external pull requests.

Closes #14

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Vonng