bpo-36793: Remove unneeded __str__ definitions. (GH-13081)

Classes that define __str__ the same as __repr__ can
just inherit it from object.
diff --git a/Objects/boolobject.c b/Objects/boolobject.c
index b92fafe..508ea61 100644
--- a/Objects/boolobject.c
+++ b/Objects/boolobject.c
@@ -147,7 +147,7 @@
     0,                                          /* tp_as_mapping */
     0,                                          /* tp_hash */
     0,                                          /* tp_call */
-    bool_repr,                                  /* tp_str */
+    0,                                          /* tp_str */
     0,                                          /* tp_getattro */
     0,                                          /* tp_setattro */
     0,                                          /* tp_as_buffer */