wxWidgets 3.3.2 changed MSWGetStyle to add WS_CAPTION when
wxMINIMIZE_BOX/wxMAXIMIZE_BOX/wxCLOSE_BOX is set. This caused
DefWindowProc to subtract the caption height in WM_NCCALCSIZE for
maximized windows, shrinking the client area and creating a gap
above the taskbar.
Fix by handling WM_NCCALCSIZE for the maximized case explicitly
(strip only border overshoot, not caption) and removing the now
unnecessary wxEVT_MAXIMIZE workaround.