Store menus titles in menus themselves in wxOSX.

Store menus titles in menus themselves in wxOSX.

Get rid of wxMenuBar::m_titles array which doesn't seem to be needed and just
store the titles in the menus themselves instead. This makes wxMenu::GetTitle()
work as in the other ports and fixes unit test failures in menu test.

It also makes it unnecessary to duplicate the base class Find[Menu]Item()
methods in wxOSX wxMenuBar so simply remove them entirely.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66402 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775