-CASPolicies or -allowCasPolicies flag is deprecated in SharePoint 2013. So the new behavior is if -CASPolicies (for PowerShell with Install-SPSolution) or -allowCasPolicies (for stsadm) is specified, regardless of whether or not the solution actually contains CAS policy, you will get the message below.

"Solutions no longer support deploying Code Access Security (CAS) policy so any CAS policy specified in solution "{0}" was skipped and not deployed. Deploy this solution without the -CASPolicies flag to suppress this warning."

The existing alert that logs to ULS that CAS policy is detected and getting skipped is still in place so if  you removes the -CASPolicies (for PowerShell) or -allowCasPolicies (for stsadm) flag to suppress the above warning, you will continue to get an entry in the ULS log explaining their CAS policy has been skipped until you actually remove the CAS policy from the solution (You can verify it in the manifest.xml of WSP).