s4-dsdb: moved checking of duplicate member entries to repl_meta_data.c

s4-dsdb: moved checking of duplicate member entries to repl_meta_data.c

the samldb checks failed to account for the possibility of a member
being removed and added in the same modify operation. This happens
(for example) when dbcheck is fixing a SID in a DN.

The repl_meta_data.c code already has this check, it just wasn't
giving the right specialised error code for the 'member' attribute

Pair-Programmed-With: Andrew Bartlett <abartlet@samba.org>
Pair-Programmed-With: Amitay Isaacs <amitay@gmail.com>