fix: remove Py_single_input macro redefinition in PyMethodBase.h

Remove the `#define Py_single_input 256` from the public header to
avoid a `-Wmacro-redefined` warning when CPython's compile.h is
included after the precompiled header already defines the macro.
The default argument now uses the literal value with a comment.

Author: chrisburr

tmva/pymva/inc/TMVA/PyMethodBase.h

@@ -34,7 +34,6 @@ class TH1D;
 #ifndef PyObject_HEAD
 struct _object;
 typedef _object PyObject;
-#define Py_single_input 256
 #endif
 
 namespace TMVA {
@@ -111,7 +110,7 @@ namespace TMVA {
       PyObject *fPyReturn; // python return data
 
    protected:
-      void PyRunString(TString code, TString errorMessage="Failed to run python code", int start=Py_single_input); // runs python code from string in local namespace with error handling
+      void PyRunString(TString code, TString errorMessage="Failed to run python code", int start=256 /* Py_single_input */); // runs python code from string in local namespace with error handling
 
    private:
       static PyObject *fModuleBuiltin;