[TMVA experimental] Use C++11 syntax for template with default parameters
[TMVA experimental] Use C++11 syntax for template with default parameters

* In C++17 you can strip the empty brackets <> if all template arguments
are given by default. Don't use this syntax in the tests.

karies/root,olifre/root,karies/root,root-mirror/root,root-mirror/root,karies/root,karies/root,root-mirror/root,root-mirror/root,karies/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,karies/root,olifre/root,karies/root,olifre/root,olifre/root,root-mirror/root,karies/root,olifre/root,karies/root,root-mirror/root,olifre/root,karies/root,karies/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,olifre/root