bpo-35081: Cleanup pystate.c and pystate.h (GH-10240)

* Remove _PyThreadState_Current
* Replace GET_TSTATE() with PyThreadState_GET()
* Replace GET_INTERP_STATE() with _PyInterpreterState_GET_UNSAFE()
* Replace direct access to _PyThreadState_Current with
  PyThreadState_GET()
* Replace _PyThreadState_Current with
  _PyRuntime.gilstate.tstate_current
* Rename SET_TSTATE() to _PyThreadState_SET(), name more
  consistent with _PyThreadState_GET()
* Update outdated comments
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index ee65695..363d902 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -1314,8 +1314,8 @@
     /* We can arrive here with a NULL tstate during initialization: try
        running "python -Wi" for an example related to string interning.
        Let's just hope that no exception occurs then...  This must be
-       _PyThreadState_Current and not PyThreadState_GET() because in debug
-       mode, the latter complains if tstate is NULL. */
+       PyThreadState_GET() and not PyThreadState_Get() because the latter
+       abort Python if tstate is NULL. */
     tstate = PyThreadState_GET();
     if (tstate != NULL && tstate->curexc_type != NULL) {
         /* preserve the existing exception */