bpo-39542: Simplify _Py_NewReference() (GH-18332)

* Remove _Py_INC_REFTOTAL and _Py_DEC_REFTOTAL macros: modify
  directly _Py_RefTotal.
* _Py_ForgetReference() is no longer defined if the Py_TRACE_REFS
  macro is not defined.
* Remove _Py_NewReference() implementation from object.c:
  unify the two implementations in object.h inline function.
* Fix Py_TRACE_REFS build: _Py_INC_TPALLOCS() macro has been removed.
diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
index 00151b8..5334eca 100644
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -2948,8 +2948,12 @@
         return (*pv == NULL) ? -1 : 0;
     }
     /* XXX UNREF/NEWREF interface should be more symmetrical */
-    _Py_DEC_REFTOTAL;
+#ifdef Py_REF_DEBUG
+    _Py_RefTotal--;
+#endif
+#ifdef Py_TRACE_REFS
     _Py_ForgetReference(v);
+#endif
     *pv = (PyObject *)
         PyObject_REALLOC(v, PyBytesObject_SIZE + newsize);
     if (*pv == NULL) {