Don't document wxVector<>::reverse_iterator.

Don't document wxVector<>::reverse_iterator.

Documenting just this class but not iterator (and const_iterator) is
inconsistent but documenting all of them is too much mostly useless work as
all iterators (of the same category) have the same interface anyhow. So just
remove the documentation of reverse_iterator for now.

See #2585.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70484 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775