Fix menu item destruction broken by r75250.

The menu items were not removed from the menu any longer when they were
deleted or destroyed after the changes in this revision.

Fix this by calling the public Remove(), which does the right thing, instead
of the private DoRemove(), which only does part of the job of removing the
item, in DoDelete() and DoDestroy().

See #3424.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75290 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775