bpo-42519: Replace PyObject_MALLOC() with PyObject_Malloc() (GH-23587)

No longer use deprecated aliases to functions:

* Replace PyObject_MALLOC() with PyObject_Malloc()
* Replace PyObject_REALLOC() with PyObject_Realloc()
* Replace PyObject_FREE() with PyObject_Free()
* Replace PyObject_Del() with PyObject_Free()
* Replace PyObject_DEL() with PyObject_Free()
diff --git a/Include/objimpl.h b/Include/objimpl.h
index 464b1bf..1408d05 100644
--- a/Include/objimpl.h
+++ b/Include/objimpl.h
@@ -38,7 +38,7 @@ Functions and macros for modules that implement new object types.
    object with room for n items.  In addition to the refcount and type pointer
    fields, this also fills in the ob_size field.
 
- - PyObject_Del(op) releases the memory allocated for an object.  It does not
+ - PyObject_Free(op) releases the memory allocated for an object.  It does not
    run a destructor -- it only frees the memory.  PyObject_Free is identical.
 
  - PyObject_Init(op, typeobj) and PyObject_InitVar(op, typeobj, n) don't
@@ -103,6 +103,8 @@ PyAPI_FUNC(void) PyObject_Free(void *ptr);
 
 
 // Deprecated aliases only kept for backward compatibility.
+// PyObject_Del and PyObject_DEL are defined with no parameter to be able to
+// use them as function pointers (ex: tp_free = PyObject_Del).
 #define PyObject_MALLOC         PyObject_Malloc
 #define PyObject_REALLOC        PyObject_Realloc
 #define PyObject_FREE           PyObject_Free