cext: remove some conditional preprocessor defines

cext: remove some conditional preprocessor defines

We may want to inline these defines. But for now, getting rid of the
Python 2 support is a step forward.

Differential Revision: https://phab.mercurial-scm.org/D12224

--- a/mercurial/cext/manifest.c	Sun Feb 20 15:43:30 2022 -0700
+++ b/mercurial/cext/manifest.c	Sun Feb 20 15:44:39 2022 -0700
@@ -317,12 +317,7 @@
 	return ret;
 }
 
-#ifdef IS_PY3K
 #define LAZYMANIFESTENTRIESITERATOR_TPFLAGS Py_TPFLAGS_DEFAULT
-#else
-#define LAZYMANIFESTENTRIESITERATOR_TPFLAGS Py_TPFLAGS_DEFAULT \
-	| Py_TPFLAGS_HAVE_ITER
-#endif
 
 static PyTypeObject lazymanifestEntriesIterator = {
 	PyVarObject_HEAD_INIT(NULL, 0) /* header */
@@ -365,12 +360,7 @@
 	return PyBytes_FromStringAndSize(l->start, pl);
 }
 
-#ifdef IS_PY3K
 #define LAZYMANIFESTKEYSITERATOR_TPFLAGS Py_TPFLAGS_DEFAULT
-#else
-#define LAZYMANIFESTKEYSITERATOR_TPFLAGS Py_TPFLAGS_DEFAULT \
-	| Py_TPFLAGS_HAVE_ITER
-#endif
 
 static PyTypeObject lazymanifestKeysIterator = {
 	PyVarObject_HEAD_INIT(NULL, 0) /* header */
@@ -955,11 +945,7 @@
 	{NULL},
 };
 
-#ifdef IS_PY3K
 #define LAZYMANIFEST_TPFLAGS Py_TPFLAGS_DEFAULT
-#else
-#define LAZYMANIFEST_TPFLAGS Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_SEQUENCE_IN
-#endif
 
 static PyTypeObject lazymanifestType = {
 	PyVarObject_HEAD_INIT(NULL, 0) /* header */