s4/replmd delete: optimise attribute preservation with binary search

s4/replmd delete: optimise attribute preservation with binary search

When we get here it is very likely that the attribute will not be
preserved, as the preserved ones should have had the flag set, but we
still end up loking through the whole list to confirm. With a binary
search, we end up looking at ~5 attributes to confirm.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>