[1578] unrelated doc fix: corrected description of MEM_SUPER_STOP log.

src/lib/datasrc/datasrc_messages.mes

@@ -376,7 +376,7 @@ Some resource types are singletons -- only one is allowed in a domain
 % DATASRC_MEM_SUCCESS query for '%1/%2' successful
 Debug information. The requested record was found.
 
-% DATASRC_MEM_SUPER_STOP stopped at superdomain '%1', domain '%2' is empty
+% DATASRC_MEM_SUPER_STOP stopped at subdomain of '%1', meaning it's empty
 Debug information. The search stopped at a superdomain of the requested
 domain. The domain is an empty nonterminal, therefore it is treated  as NXRRSET
 case (eg. the domain exists, but it doesn't have the requested record type).

src/lib/datasrc/memory_datasrc.cc

@@ -697,7 +697,7 @@ struct InMemoryZoneFinder::InMemoryZoneFinderImpl {
                 if (node_path.getLastComparisonResult().getRelation() ==
                     NameComparisonResult::SUPERDOMAIN) {
                     LOG_DEBUG(logger, DBG_TRACE_DATA, DATASRC_MEM_SUPER_STOP).
-                        arg(node_path.getAbsoluteName()).arg(name);
+                        arg(name);
                     return (createFindResult(NXRRSET, ConstRRsetPtr(), false));
                 }