bpo-29464: Rename METH_FASTCALL to METH_FASTCALL|METH_KEYWORDS and make (#1955)

the bare METH_FASTCALL be used for functions with positional-only
parameters.
diff --git a/Modules/_elementtree.c b/Modules/_elementtree.c
index 82df58f..eaa9e87 100644
--- a/Modules/_elementtree.c
+++ b/Modules/_elementtree.c
@@ -2774,7 +2774,7 @@
 } XMLParserObject;
 
 static PyObject*
-_elementtree_XMLParser_doctype(XMLParserObject *self, PyObject **args, Py_ssize_t nargs, PyObject *kwnames);
+_elementtree_XMLParser_doctype(XMLParserObject *self, PyObject **args, Py_ssize_t nargs);
 static PyObject *
 _elementtree_XMLParser_doctype_impl(XMLParserObject *self, PyObject *name,
                                     PyObject *pubid, PyObject *system);