Remove validation check limiting None platform to SNO

Currently there are validation checks for platform None in OptionalInstallConfig that limits the None platform to 1 control plane replica, 0 compute replicas, and the NetworkType to OVNKubernetes.

These validation should be removed so that the None platform can be installed on clusters of any configuration.

Acceptance Criteria:

• SNO cluster should still continue to work.
• SNO validation should still check only OVNKubernetes network type is allowed
• A compact or HA cluster can be installed with platform None, given the user has configured and deployed an external load balancer.