gh-101100: Fix Sphinx warnings in c-api/structures.rst (#113564)

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>
Co-authored-by: Petr Viktorin <encukou@gmail.com>

Doc/c-api/structures.rst

@@ -551,11 +551,11 @@ The following flags can be used with :c:member:`PyMemberDef.flags`:
    from ``PyObject``.
 
    Can only be used as part of :c:member:`Py_tp_members <PyTypeObject.tp_members>`
-   :c:type:`slot <PyTypeSlot>` when creating a class using negative
+   :c:type:`slot <PyType_Slot>` when creating a class using negative
    :c:member:`~PyType_Spec.basicsize`.
    It is mandatory in that case.
 
-   This flag is only used in :c:type:`PyTypeSlot`.
+   This flag is only used in :c:type:`PyType_Slot`.
    When setting :c:member:`~PyTypeObject.tp_members` during
    class creation, Python clears it and sets
    :c:member:`PyMemberDef.offset` to the offset from the ``PyObject`` struct.
@@ -693,7 +693,8 @@ Defining Getters and Setters
 
    .. c:member:: setter set
 
-      Optional C function to set or delete the attribute, if omitted the attribute is readonly.
+      Optional C function to set or delete the attribute.
+      If ``NULL``, the attribute is read-only.
 
    .. c:member:: const char* doc
 
@@ -703,18 +704,18 @@ Defining Getters and Setters
 
       Optional function pointer, providing additional data for getter and setter.
 
-   The ``get`` function takes one :c:expr:`PyObject*` parameter (the
-   instance) and a function pointer (the associated ``closure``)::
+.. c:type:: PyObject *(*getter)(PyObject *, void *)
 
-      typedef PyObject *(*getter)(PyObject *, void *);
+   The ``get`` function takes one :c:expr:`PyObject*` parameter (the
+   instance) and a function pointer (the associated ``closure``):
 
    It should return a new reference on success or ``NULL`` with a set exception
    on failure.
 
-   ``set`` functions take two :c:expr:`PyObject*` parameters (the instance and
-   the value to be set) and a function pointer (the associated ``closure``)::
+.. c:type:: int (*setter)(PyObject *, PyObject *, void *)
 
-      typedef int (*setter)(PyObject *, PyObject *, void *);
+   ``set`` functions take two :c:expr:`PyObject*` parameters (the instance and
+   the value to be set) and a function pointer (the associated ``closure``):
 
    In case the attribute should be deleted the second parameter is ``NULL``.
    Should return ``0`` on success or ``-1`` with a set exception on failure.

Doc/tools/.nitignore

@@ -14,7 +14,6 @@ Doc/c-api/memoryview.rst
 Doc/c-api/module.rst
 Doc/c-api/object.rst
 Doc/c-api/stable.rst
-Doc/c-api/structures.rst
 Doc/c-api/sys.rst
 Doc/c-api/type.rst
 Doc/c-api/typeobj.rst