Simplify wxMSW wxMenuBar title management.

Simplify wxMSW wxMenuBar title management.

Store the titles of the menu bar menus in the menu objects themselves. This
makes wxMenu::GetTitle() return the expected result for them (which also fixes
the current unit test failures for wxMSW) and makes wxMenuBar code simpler.

This removes the wxMenuInfo class which existed for XTI purposes only but as
it was apparently unfinished and MSW-specific it shouldn't be a big loss.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66178 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775