Obsolete CLAUSEFLAG NEWDEFAULT

Obsolete CLAUSEFLAG NEWDEFAULT

The 'new default' option was introduced in 2002 to signal that a
default option had changed its default value, in this specific case
the value for 'auth-nxdomain'. However, this default has been unchanged
for 18 years now, and logging that the default has changed does not
have significant value nowadays.

This is also a good example that the clause flag 'new default' is
broken: it is easy to get out of date.

It is also easy to forget, because we have changed the default value
for 'max-stale-ttl' and haven't been flagging it with 'new default'

Also, if the operator cares for a specific value it should set it
explicitly. Using the default is telling the software: use whatever
you think is best, and this may change over time. Default value
changes should be mentioned in the release note, but do not require
further special treatment.