Removes a subclass callback from a window
#include <WinAPIShellEx.au3>
_WinAPI_RemoveWindowSubclass ( $hWnd, $pSubclassProc, $idSubClass )
| $hWnd | Handle of the window being subclassed. | 
| $pSubclassProc | A pointer to a window procedure. This pointer and the subclass ID uniquely identify this subclass callback. (See MSDN for more information)  | 
| $idSubClass | The subclass ID. | 
| Success: | True. | 
| Failure: | False. | 
_WinAPI_SetWindowSubclass, _WinAPI_DefSubclassProc
Search RemoveWindowSubclass in MSDN Library.
#include "Extras\WMDebug.au3"
#include <GUIConstantsEx.au3>
#include <WinAPIShellEx.au3>
OnAutoItExitRegister('OnAutoItExit')
; Create GUI
Global $g_hForm = GUICreate('Test ' & StringReplace(@ScriptName, '.au3', '()'))
; Register DLL callback that will be used as window subclass procedure
Global $g_hDll = DllCallbackRegister('_SubclassProc', 'lresult', 'hwnd;uint;wparam;lparam;uint_ptr;dword_ptr')
Global $g_pDll = DllCallbackGetPtr($g_hDll)
; Install window subclass callback
_WinAPI_SetWindowSubclass($g_hForm, $g_pDll, 1000, 0)
GUISetState(@SW_SHOW)
Do
Until GUIGetMsg() = $GUI_EVENT_CLOSE
Func _SubclassProc($hWnd, $iMsg, $wParam, $lParam, $iID, $pData)
    #forceref $iID, $pData
    ; Declared in WMDebug.au3
    _WM_Debug($hWnd, $iMsg, $wParam, $lParam)
    Return _WinAPI_DefSubclassProc($hWnd, $iMsg, $wParam, $lParam)
EndFunc   ;==>_SubclassProc
Func OnAutoItExit()
    _WinAPI_RemoveWindowSubclass($g_hForm, $g_pDll, 1000)
    DllCallbackFree($g_hDll)
EndFunc   ;==>OnAutoItExit