Revert "Make wxMSW stack walking methods work with Unicode identifiers."

This reverts r74817 because it broke compilation with VC8 and it doesn't seem
obvious to fix this.

See #15138, closes #15500.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74820 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775