Hide the Python module implementation init function

Python extension modules only need to export the PyInit function.
Any other C functions are merely part of the module implementation,
and can therefore be kept private.

Wrapping/Tools/vtkWrapPythonInit.c

@@ -36,8 +36,6 @@ static void CreateImplFile(
 {
   int i;
 
-  const char* dllexp = "VTK_ABI_EXPORT ";
-
   fprintf(fout, "// Generated by vtkWrapPythonInit in VTK/Wrapping\n");
   fprintf(fout, "#include \"vtkPythonUtil.h\"\n");
   fprintf(fout, "#include \"vtkSystemIncludes.h\"\n");
@@ -68,8 +66,8 @@ static void CreateImplFile(
   fprintf(fout, "  nullptr  // m_free\n");
   fprintf(fout, "};\n");
 
-  fprintf(fout, "extern  \"C\" {%sPyObject *real_init%s(const char * /*unused*/); }\n\n", dllexp,
-    libName);
+  fprintf(fout, "extern  \"C\" {%s PyObject *real_init%s(const char * /*unused*/); }\n\n",
+    "VTK_ABI_HIDDEN", libName);
 
   fprintf(fout, "PyObject *real_init%s(const char * /*unused*/)\n{\n", libName);