Yet another fix after wxMenu::Remove() refactoring.

wxMenu::Remove() was still broken in wxMSW after r75250, even with the fix in
r75290, as wxMSW code relied on the item still being present in
wxMenu::m_items.

Delay removing it from there until after DoRemove() call to fix this.

See #3424.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75297 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775