Which users are not using Visio and Project licenses

There's no way to obtain such information from PowerShell. Best you can do is check whether they have a valid license applied, the usage information needs to come from someplace else, such as any report you can obtain from Project, or the Office 365 Unified Audit log or similar.

Can you expand more on how to find this information using Office 365 Unified Audit log ?

You'll basically have to search for "login" events, and for each of those look at the client info (if such is available) in order to determine whether the request came from Visio or Project. Keep in mind that with Modern authentication and the current token lifetimes, one a user successfully authenticates, it might be *months* before you see another event, and in the meantime he can keep accessing/using the service just fine.

Check the documentation for more info: https://docs.microsoft.com/en-us/office365/securitycompliance/detailed-properties-in-the-office-365-audit-log

if you have a tool such as SCCM, there are canned reports in there.  From SCCM you will use software inventory and then you can create a collection of users that have not used project (or visio) in say 30 days and apply a script to that collection to uninstall the offending program.  Without using some sort of mgmt. tool like SCCM or Altiris there is no real way to do what you are asking.
  Sorry