Cleanup: replace UNUSED macro with commented args in C++ code

This is the conventional way of dealing with unused arguments in C++,
since it works on all compilers.

Regex find and replace: `UNUSED\((\w+)\)` -> `/*$1*/`

source/blender/freestyle/intern/python/UnaryFunction1D/BPy_UnaryFunction1DVec2f.cpp

@@ -134,14 +134,14 @@ PyDoc_STRVAR(integration_type_doc,
              "\n"
              ":type: :class:`IntegrationType`");
 
-static PyObject *integration_type_get(BPy_UnaryFunction1DVec2f *self, void *UNUSED(closure))
+static PyObject *integration_type_get(BPy_UnaryFunction1DVec2f *self, void * /*closure*/)
 {
   return BPy_IntegrationType_from_IntegrationType(self->uf1D_vec2f->getIntegrationType());
 }
 
 static int integration_type_set(BPy_UnaryFunction1DVec2f *self,
                                 PyObject *value,
-                                void *UNUSED(closure))
+                                void * /*closure*/)
 {
   if (!BPy_IntegrationType_Check(value)) {
     PyErr_SetString(PyExc_TypeError, "value must be an IntegrationType");