Remove unused centos7 chef multinode job
This job is defined but nowhere used, remove it.
node:
- centos-7
- ubuntu-xenial
- - 'gate-{name}-chef-rake-integration-multinode-{node-release}-nv':
- node-release: centos-7
- node: centos-7-2-node
- 'gate-{name}-chef-rake-integration-multinode-{node-release}-nv':
node-release: ubuntu-xenial
node: ubuntu-xenial-2-node
