TMVA code is not thread safe so modules must be legacy

Helgrind identified ElectronIdMVABased and GoodSeedProducer as interacting
with the singleton buried within TMVA at event time. This is not thread
safe so these modules must be downgraded to legacy.
A quick review of TMVA actually shows that if more than one TMVA::Reader
is used in an application that it can lead to a segmentation fault
because of poor ownership of the singleton within TMVA.
Merge pull request #3906 from Dr15Jones/tmvaIsNotThreadSafe

Multithreading -- TMVA code is not thread safe so modules must be legacy