Remove check for DTS_SHORTDATECENTURYFORMAT

<https://msdn.microsoft.com/en-us/library/windows/desktop/bb761728(v=vs.85).aspx>

src/msw/datectrl.cpp

@@ -74,11 +74,9 @@ WXDWORD wxDatePickerCtrl::MSWGetStyle(long style, WXDWORD *exstyle) const
         styleMSW |= DTS_UPDOWN;
     //else: drop down by default
 
-#ifdef DTS_SHORTDATECENTURYFORMAT
     if ( style & wxDP_SHOWCENTURY )
         styleMSW |= DTS_SHORTDATECENTURYFORMAT;
     else
-#endif // DTS_SHORTDATECENTURYFORMAT
         styleMSW |= DTS_SHORTDATEFORMAT;
 
     if ( style & wxDP_ALLOWNONE )