Remove the vestigial OpenShift client role

[dholt]

Summary

• Remove the vestigial openshift client role, the bootstrap-openshift.yml playbook, its imports in k8s-cluster.yml and the GPU Operator playbook, and the meta-dependencies from the three GPU roles.
• Nothing consumes it: the GPU Operator, device plugin, and GPU feature discovery roles deploy exclusively through Helm; no playbook or role uses the Ansible k8s modules against the virtualenv this role created; and the roles that need EPEL on Red Hat install it themselves. The role installed the deprecated OpenShift Python client for a module usage that no longer exists in the repository.
• The legacy RoCE backend role is unaffected — it installs its own client inside its own tasks.

Validation

• git diff --check; YAML parse of changed files; full role lint (0 failures); playbooks/k8s-cluster.yml syntax check passes.
• Removal of dead code only: no default deployment path executes any of the removed logic's effects.