[CMake][Exp PyROOT] Remove part used for previous MultiPython incremental
[CMake][Exp PyROOT] Remove part used for previous MultiPython incremental

This part was here to avoid to specify many variables for the previous
incremental way of build with multiple python versions.

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