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

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

Author: methane

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 */