Remove compile-time checks for always defined WM_XXX in wxMSW

The symbols in question are present at least since XP, and most of them since
Windows 2000, so remove preprocessor checks for them, they shouldn't be needed
when any remotely current compiler/SDK.

src/msw/spinctrl.cpp

@@ -101,12 +101,10 @@ wxBuddyTextWndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
         case WM_DEADCHAR:
         case WM_KEYUP:
         case WM_KEYDOWN:
-#ifdef WM_HELP
         // we need to forward WM_HELP too to ensure that the context help
         // associated with wxSpinCtrl is shown when the text control part of it
         // is clicked with the "?" cursor
         case WM_HELP:
-#endif
             {
                 WXLRESULT result;
                 if ( spin->MSWHandleMessage(&result, message, wParam, lParam) )