These files are supposed to have different permissions (0660 for
btmp and 0664 for wtmp), which isn't possible using a single united
base::newsyslog::config stanza.  Separate them into two stanzas
with the correct permissions.

The deprecated classes base::newsyslog::messages::sa and
base::newsyslog::messages::sa::override have been deleted.  Global
overrides for the default base::newsyslog behavior should be put into
the local defaults module instead.