gh-129185: Simplify PyTraceMalloc_Track() (#129256)

Since tracemalloc uses PyMutex, it becomes safe to use TABLES_LOCK()
even after _PyTraceMalloc_Fini(): remove the "pre-check" in
PyTraceMalloc_Track() and PyTraceMalloc_Untrack().

PyTraceMalloc_Untrack() no longer needs to acquire the GIL.

_PyTraceMalloc_Fini() can be called earlier during Python
finalization.

Python/pylifecycle.c

@@ -2113,7 +2113,7 @@ _Py_Finalize(_PyRuntimeState *runtime)
 
     /* Disable tracemalloc after all Python objects have been destroyed,
        so it is possible to use tracemalloc in objects destructor. */
-    _PyTraceMalloc_Stop();
+    _PyTraceMalloc_Fini();
 
     /* Finalize any remaining import state */
     // XXX Move these up to where finalize_modules() is currently.
@@ -2166,7 +2166,6 @@ _Py_Finalize(_PyRuntimeState *runtime)
 
     finalize_interp_clear(tstate);
 
-    _PyTraceMalloc_Fini();
 
 #ifdef Py_TRACE_REFS
     /* Display addresses (& refcnts) of all objects still alive.