Removed unused variable to avoid valgrind error in SoftElectronMVAEstimator

A member variable which was not being used was being compared against and
valgrind was flagging it as an error. It was trivial to comment out the
variable.
Merge pull request #4129 from Dr15Jones/valgrindFixSoftElectronMVAEstimator

Removed unused variable to avoid valgrind error in SoftElectronMVAEstimator