Remove CAM3 as a compset or configure option

[nusbaume]

Issue Type

Code Clean-up

Issue Description

After PR #890 CAM development is no longer able to replicate CAM3 physics regardless of settings, and thus CAM3 is no longer considered a supported physics configuration. Given this, it would be good to officially remove CAM3 from the list of possible compsets, as well as a possible physics package option for CESM3.

This would likely need to be done after all CAM3 regression tests have also been removed, as described in issue #258.

Will this change answers?

No

Will you be implementing this yourself?

Any CAM SE can do this