Don't use a destroy event handler to disconnect the native control's delegate as...

Don't use a destroy event handler to disconnect the native control's delegate as the destroy event propagates and can cause the TLW to remove its delegate at unexpected times, such as when a child control is destroyed but the TLW remains active. Instead, do it in response to the Destroy() call.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63051 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775