docs: Deprecate "map untrusted to domain"

docs: Deprecate "map untrusted to domain"

The implementation of this parameter depends on Samba to enumerate
trusted domains. In an active directory environment, we don't know of
a good way to enumerate all domains that we have to accept as trusted,
in particular with multiple forests, one-way and external trusts. We
hope to replace this parameter in the future with something that matches
Windows behaviour better, after the deprecation phase of this parameter
is over and we can remove it.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>