Hide page removed from wxAuiNotebook

It doesn't make sense to leave the page shown, and overlapping the
remaining pages, after removing it.

Closes https://github.com/wxWidgets/wxWidgets/pull/1742

docs/changes.txt

@@ -90,6 +90,9 @@ Changes in behaviour not resulting in compilation errors
 - wxListCtrl::GetItemState() in wxMSW now checks the passed in item index for
   validity, as the generic version under the other platforms already did.
 
+- wxAuiNotebook::RemovePage() now hides the removed page, so it needs to be
+  shown again if it is reused in another place.
+
 
 Changes in behaviour which may result in build errors
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