LIBSVM_VERSION is passed as a string to the compiler, but evaluated as uint64_t in the code

Related to bob.extension#58 (closed).

In the setup.py, the LIBSVM_VERSION is passed as a compiler parameter in form of a string "a.b". However, in the source code, it is evaluated as a uint64_t, e.g.: https://gitlab.idiap.ch/bob/bob.learn.libsvm/blob/d8fd7b158bf5d6225d1e472bec20812c493b28be/bob/learn/libsvm/cpp/machine.cpp#L386

Apparently, the parameter passed on the compiler command line is (luckily) ignored, but the one provided in the svm header file is used instead. So, we should remove the one passed on the command line.