Need to remove old CAM suite definition files

[nusbaume]

There are currently three old CAM Suite Definition Files (suite_cam4.xml, suite_cam6.xml, and suite_cam6_silhs.xml) that were written years ago as a scoping exercise, and are likely unable to actually work as real CAM-SIMA SDFs. Thus while useful as a reference during CAM CCPP-conversions, their presence in this repo is causing confusion, especially for new users and developers.

Given this, it would be great to remove these three files from this repo, especially before a "real" suite_cam4.xml file is added. I have already copied the files to a backup repo here:

https://github.com/NCAR/CAM-SIMA_backups/tree/main/old_suite_files

So these files can likely be deleted from atmospheric_physics whenever someone gets the chance (it should have no impact on any tests or host model results).