[ironic] stepping down from core

Hello folks, As you might have noticed my contribution to ironic has dropped to almost 0 during the last three months. My current job responsibilities have changed, and I can't dedicate the time needed to be a core reviewer at this time. I will still be around and at some point might get back to contributing to ironic, but for now I'd like to request to be removed from the core reviewers group. Thank you, Vlad