Scanner classes should use the same constants as the module defines

I just noticed that scanner errors from ClamAVDaemonScanner::scan() were not getting picked up by the module because there was a constant with a hex value that the module wasn't listening for. This made me think that the scan methods should be reporting back the same constants that the module is expecting to avoid any confusion - it's the API that the module is dictating.

Anyway, this patch removes the custom constants and sends scan responses using the constants that the module is expecting.