ffi cleanup: add missing deprecation

src/ffi/descrobject.rs

@@ -71,6 +71,7 @@ extern "C" {
 /// Helper initial value of [`PyGetSetDef`] for a Python class.
 ///
 /// Not present in `cpython/Include/descrobject`.
+#[deprecated(note = "not present in Python headers; to be removed")]
 pub const PyGetSetDef_INIT: PyGetSetDef = PyGetSetDef {
     name: ptr::null_mut(),
     get: None,

src/pyclass.rs

@@ -333,6 +333,7 @@ fn py_class_method_defs<T: PyMethods>() -> (
     (new, call, defs)
 }
 
+#[allow(deprecated)]
 fn py_class_properties<T: PyClass>() -> Vec<ffi::PyGetSetDef> {
     let mut defs = std::collections::HashMap::new();