user32: Use NtUserMessageCall for SendMessageCallbackA implementation.

dlls/win32u/message.c

@@ -1474,7 +1474,7 @@ static int peek_message( MSG *msg, HWND hwnd, UINT first, UINT last, UINT flags,
  *
  * Process all pending sent messages.
  */
-void process_sent_messages(void)
+static void process_sent_messages(void)
 {
     MSG msg;
     peek_message( &msg, 0, 0, 0, PM_REMOVE | PM_QS_SENDMESSAGE, 0 );

dlls/win32u/sysparams.c

@@ -4643,9 +4643,6 @@ ULONG_PTR WINAPI NtUserCallNoParam( ULONG code )
     /* temporary exports */
     case NtUserExitingThread:
         exiting_thread_id = GetCurrentThreadId();
-    case NtUserProcessSentMessages:
-        process_sent_messages();
-        return 0;
     case NtUserThreadDetach:
         thread_detach();
         return 0;

dlls/win32u/win32u_private.h

@@ -350,7 +350,6 @@ extern HMENU get_menu( HWND hwnd ) DECLSPEC_HIDDEN;
 /* message.c */
 extern LRESULT dispatch_message( const MSG *msg, BOOL ansi ) DECLSPEC_HIDDEN;
 extern BOOL kill_system_timer( HWND hwnd, UINT_PTR id ) DECLSPEC_HIDDEN;
-extern void process_sent_messages(void) DECLSPEC_HIDDEN;
 extern BOOL reply_message_result( LRESULT result, MSG *msg ) DECLSPEC_HIDDEN;
 extern NTSTATUS send_hardware_message( HWND hwnd, const INPUT *input, const RAWINPUT *rawinput,
                                        UINT flags ) DECLSPEC_HIDDEN;

include/ntuser.h

@@ -140,7 +140,6 @@ enum
     NtUserReleaseCapture,
     /* temporary exports */
     NtUserExitingThread,
-    NtUserProcessSentMessages,
     NtUserThreadDetach,
 };