Issue #26558: Remove useless check in tracemalloc

The first instruction of tracemalloc_add_trace() is traceback_new() which
already checks the GIL.
diff --git a/Modules/_tracemalloc.c b/Modules/_tracemalloc.c
index 226a473..d62e682 100644
--- a/Modules/_tracemalloc.c
+++ b/Modules/_tracemalloc.c
@@ -439,10 +439,6 @@
     trace_t trace;
     int res;
 
-#ifdef WITH_THREAD
-    assert(PyGILState_Check());
-#endif
-
     traceback = traceback_new();
     if (traceback == NULL)
         return -1;