Don't assert if Ctrl+Tab is pressed inside a wxGTK window

Ignore the WinChange flag in DoNavigateIn() to fix an assertion that happened
when pressing Ctrl+Tab with the generic wxListCtrl having focus.

This seems to be consistent with pressing Ctrl+Tab elsewhere, e.g. when
cycling between buttons in a dialog.

src/gtk/window.cpp

@@ -3818,14 +3818,6 @@ void wxWindowGTK::DoMoveInTabOrder(wxWindow *win, WindowOrder move)
 
 bool wxWindowGTK::DoNavigateIn(int flags)
 {
-    if ( flags & wxNavigationKeyEvent::WinChange )
-    {
-        wxFAIL_MSG( wxT("not implemented") );
-
-        return false;
-    }
-    else // navigate inside the container
-    {
     wxWindow *parent = wxGetTopLevelParent((wxWindow *)this);
     wxCHECK_MSG( parent, false, wxT("every window must have a TLW parent") );
 
@@ -3837,7 +3829,6 @@ bool wxWindowGTK::DoNavigateIn(int flags)
     g_signal_emit_by_name(parent->m_widget, "focus", dir, &rc);
 
     return rc != 0;
-    }
 }
 
 bool wxWindowGTK::GTKWidgetNeedsMnemonic() const