bpo-29304: Simplify dict lookup functions (GH-2407)

* remove hashpos parameter from lookdict functions.
* remove many duplicated code from lookdict functions.

Objects/dict-common.h

@@ -12,8 +12,7 @@ typedef struct {
  * -1 when no entry found, -3 when compare raises error.
  */
 typedef Py_ssize_t (*dict_lookup_func)
-(PyDictObject *mp, PyObject *key, Py_hash_t hash, PyObject **value_addr,
- Py_ssize_t *hashpos);
+    (PyDictObject *mp, PyObject *key, Py_hash_t hash, PyObject **value_addr);
 
 #define DKIX_EMPTY (-1)
 #define DKIX_DUMMY (-2)  /* Used internally */

Objects/odictobject.c

@@ -546,7 +546,7 @@ _odict_get_index_raw(PyODictObject *od, PyObject *key, Py_hash_t hash)
     PyDictKeysObject *keys = ((PyDictObject *)od)->ma_keys;
     Py_ssize_t ix;
 
-    ix = (keys->dk_lookup)((PyDictObject *)od, key, hash, &value, NULL);
+    ix = (keys->dk_lookup)((PyDictObject *)od, key, hash, &value);
     if (ix == DKIX_EMPTY) {
         return keys->dk_nentries;  /* index of new entry */
     }