Is your feature request related to a problem? Please describe.

CNMeM is not header-only and requires building a .so, which means RMM cannot be header-only. This could be resolved by just moving CNMeM's implementation to a header, but for all intents and purposes, @harrism's pool_memory_resource supersedes CNMeM.

Describe the solution you'd like

Deprecate usage of CNMeM in favor of using pool_memory_resource.

Additional context
Once we drop CNMeM, RMM can go fully header-only.