No changes, just use less long progress dialog states names.

We can refer to them using wxProgressDialog class name and not the base
wxGenericProgressDialog so do this as it is shorter and more clear because
these states have nothing to do with the generic version when used by the
native MSW implementation.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65504 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775