Recently I had to delete apex classes and since doing so using Workbench is one of the easiest way I went for it. With Workbench you can deploy a package.zip file that contains the files you want to delete in a specially formatted destructiveChanges.xml and a package.xml. When using mac I stumbled upon a problem:
problem: No package.xml found
It turned out that the standard archive command on Mac will add some metadata and folders in the .zip file that are not compatible with Workbench. To fix this you will have to create the .zip package via the terminal. You just go to the folder that contains destructiveChanges.xml and the package.xml and run:
zip -r -X destructiveChanges.zip *
This command will create the destructiveChanges.zip in a way that is compatible with Workbench. After that you can go ahead and deploy the file to Workbench. This time it will work.