Switch to using atexit for calling the cleanup function when Python terminates.

git-svn-id: http://svn.wxwidgets.org/svn/wx/wxPython@73451 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Use commands.pop()

git-svn-id: http://svn.wxwidgets.org/svn/wx/wxPython@73452 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775