Resolve provenance/allowed-set for applog_reader EXECUTE on fn_dbperf_statements_top50

MARS-803 read-only census found applog_reader EXECUTE on SECURITY DEFINER public.fn_dbperf_statements_top50(); current ACL grantor postgres. No tracked function-specific grant was found, and creator/replacement migration 010 lacks same-migration REVOKE. Clarify intended role authorization and provenance; any ACL change requires separate authorization and audit. No REVOKE authority was part of MARS-803.