Just deprecate but don't schedule for removal wxNORMAL and friends.

Deprecate the use of the old untyped constants but don't schedule them from
removal in a future wx version by removing "#if WXWIN_COMPATIBILITY_3_0" tests
around their definition and use. Provoking deprecation warnings in the code
using these constants is worth it as they are unclear and it's easy to make
mistakes when using them, but breaking this code compilation outright can't be
justified -- even in the future.

Also use more informational wxDEPRECATED_MSG() instead of a simple
wxDEPRECATED() as it might not be obvious at all how should the code be
updated exactly.

Finally, avoid the use of deprecated constants inside the library itself.

As a side effect, this closes #15814.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75565 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775