Don't require skipping "page changed" event in wxMSW wxNotebook.

Don't require skipping "page changed" event in wxMSW wxNotebook.

wxMSW wxNotebook implementation used to handle EVT_NOTEBOOK_PAGE_CHANGED event
to update the currently shown page which meant that page changing was broken
if the user code handled and didn't skip this event.

As the other ports don't require the user code to skip this event, don't do
this in wxMSW neither and always update the selected page unconditionally.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66060 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775