This basically removes the "adv" library, even though it's still
preserved for compatibility with user make/project files referring to
it.
It is done because the distinction between "adv" and "core" was never
really clear (e.g. why wxTreeCtrl was in core but wxTreeListCtrl in
adv?) and it prevented some core classes from using adv ones.
The company behind MGL toolkit (SciTech) doesn't exist since several years and
this port is not used by anybody, so remove it to ease maintenance burden.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70353 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
