Drop ruby_libvirt_gem role

Since Foreman 2.0.2 the foreman-proxy package has depended on the
libvirt gem so this isn't needed anymore.

Link: https://projects.theforeman.org/issues/30040

Author: ekohl

roles/foreman_provisioning/meta/main.yml

@@ -1,7 +1,6 @@
 ---
 dependencies:
   - role: hammer_credentials
-  - role: ruby_libvirt_gem
   - role: foreman_installer
     foreman_installer_scenario: "{{ foreman_provisioning_scenario }}"
     foreman_installer_options: