Move file field out of generic resource type and into specific resource types

Not all resources have the same file field requirements, for example video resources.

The file field should be moved into the condition section of ocw-studio.yml

Lines 40 to 42 in 9a10fdc

    
           - label: File 
        
             name: file 
        
             widget: file

no longer relevant, now that we sync files from gdrive.