Remove `VerboseLevel:' parameter from TMVA weight files

`VerboseLevel:' parameter is not supported by newer versions of
ROOT5 and ROOT6. This blocks ROOT6 RelVals from running.

This was reported in OfflineComputingPlanningMeeting2013121.

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>