gh-112529: Revert "Use _PyThread_Id() in mimalloc in free-threaded build"

Reverts: #115488
Reason: Free-threaded Ubuntu buildbots are timing out

Author: colesbury

Include/internal/mimalloc/mimalloc/prim.h

@@ -131,13 +131,7 @@ extern bool _mi_process_is_initialized;             // has mi_process_init been
 
 static inline mi_threadid_t _mi_prim_thread_id(void) mi_attr_noexcept;
 
-#ifdef MI_PRIM_THREAD_ID
-
-static inline mi_threadid_t _mi_prim_thread_id(void) mi_attr_noexcept {
-  return MI_PRIM_THREAD_ID();
-}
-
-#elif defined(_WIN32)
+#if defined(_WIN32)
 
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>

Include/internal/pycore_mimalloc.h

@@ -20,12 +20,9 @@ typedef enum {
 #include "pycore_pymem.h"
 
 #ifdef WITH_MIMALLOC
-#  ifdef Py_GIL_DISABLED
-#    define MI_PRIM_THREAD_ID   _Py_ThreadId
-#  endif
-#  define MI_DEBUG_UNINIT     PYMEM_CLEANBYTE
-#  define MI_DEBUG_FREED      PYMEM_DEADBYTE
-#  define MI_DEBUG_PADDING    PYMEM_FORBIDDENBYTE
+#define MI_DEBUG_UNINIT     PYMEM_CLEANBYTE
+#define MI_DEBUG_FREED      PYMEM_DEADBYTE
+#define MI_DEBUG_PADDING    PYMEM_FORBIDDENBYTE
 #ifdef Py_DEBUG
 #  define MI_DEBUG 1
 #else