Remove MicroWindows support.

MicroWindows (aka Nano-X) support hasn’t been updated since 2010 and last work for it in wxWidgets happened more than 10 years ago.

src/univ/framuniv.cpp

@@ -301,9 +301,5 @@ bool wxFrame::Enable(bool enable)
 {
     if (!wxFrameBase::Enable(enable))
         return false;
-#ifdef __WXMICROWIN__
-    if (m_frameMenuBar)
-        m_frameMenuBar->Enable(enable);
-#endif
     return true;
 }