base: remove a pylint workaround that is no longer necessary

ValidationFailed is now a "real" class from Products.ERP5Type.Core.Workflow
5 jobs for erp5_drone_simulator in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

00:37:48

passed ERP5.PerformanceTest-Master

00:27:23

failed ERP5.UnitTest-Master

01:20:41

passed SlapOS.Eggs.UnitTest-Master.Python2

00:12:04

passed SlapOS.Eggs.UnitTest-Master.Python3

00:14:33