software/erp5testnode: remove useless python:part definition

this is the default
4 jobs for fix/version-up-eggs in 0 seconds (queued for 1 second)
Status Job ID Name Coverage
  External
failed ERP5.UnitTest-Master.Jerome.versionup

03:39:22

passed SlapOS.Eggs.UnitTest-Jerome.Python2

00:12:55

passed SlapOS.Eggs.UnitTest-Jerome.Python3

00:11:37

failed SlapOS.SoftwareReleases.IntegrationTest-Jerome

05:20:23