clarify no limits in (internal) searches

servers/slapd/back-bdb/search.c

servers/slapd/back-ldap/search.c

servers/slapd/back-ldbm/search.c

servers/slapd/back-passwd/search.c

servers/slapd/back-sql/search.c

servers/slapd/backglue.c

servers/slapd/limits.c

servers/slapd/overlays/pcache.c

servers/slapd/overlays/refint.c

servers/slapd/overlays/unique.c

servers/slapd/sasl.c

servers/slapd/saslauthz.c

servers/slapd/slap.h

servers/slapd/slapi/slapi_ops.c