staging: rtl8723au: Remove struct rtw_ieee802_11_elems and related code

This removes the double content tracking of data from IE elements. The
relevant code to validate IEs is moved to rtw_mlme_ext.c as this is
the only place where it is used.

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>