Drop feature test for dlopen()

With libtool being mandatory from 9.17 on, so is dlopen() (via libltdl).

bin/tests/system/dlzexternal/prereq.sh

-#!/bin/sh
-#
-# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
-#
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0. If a copy of the MPL was not distributed with this
-# file, You can obtain one at http://mozilla.org/MPL/2.0/.
-#
-# See the COPYRIGHT file distributed with this work for additional
-# information regarding copyright ownership.
-
-. $SYSTEMTESTTOP/conf.sh
-
-$FEATURETEST --have-dlopen ||  {
-        echo_i "dlopen() not supported - skipping dlzexternal test"
-        exit 255
-}
-exit 0

bin/tests/system/dyndb/prereq.sh

-#!/bin/sh
-#
-# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
-#
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0. If a copy of the MPL was not distributed with this
-# file, You can obtain one at http://mozilla.org/MPL/2.0/.
-#
-# See the COPYRIGHT file distributed with this work for additional
-# information regarding copyright ownership.
-
-. $SYSTEMTESTTOP/conf.sh
-
-$FEATURETEST --have-dlopen ||  {
-        echo_i "dlopen() not supported - skipping dyndb test"
-        exit 255
-}
-exit 0

bin/tests/system/feature-test.c

@@ -40,7 +40,6 @@ usage(void) {
 	fprintf(stderr, "	--enable-dnsrps\n");
 	fprintf(stderr, "	--gethostname\n");
 	fprintf(stderr, "	--gssapi\n");
-	fprintf(stderr, "	--have-dlopen\n");
 	fprintf(stderr, "	--have-geoip2\n");
 	fprintf(stderr, "	--have-libxml2\n");
 	fprintf(stderr, "	--ipv6only=no\n");
@@ -110,10 +109,6 @@ main(int argc, char **argv) {
 #endif /* HAVE_GSSAPI */
 	}
 
-	if (strcmp(argv[1], "--have-dlopen") == 0) {
-		return (0);
-	}
-
 	if (strcmp(argv[1], "--have-geoip2") == 0) {
 #ifdef HAVE_GEOIP2
 		return (0);

bin/tests/system/filter-aaaa/prereq.sh

-#!/bin/sh
-#
-# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
-#
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0. If a copy of the MPL was not distributed with this
-# file, You can obtain one at http://mozilla.org/MPL/2.0/.
-#
-# See the COPYRIGHT file distributed with this work for additional
-# information regarding copyright ownership.
-
-. $SYSTEMTESTTOP/conf.sh
-
-$FEATURETEST --have-dlopen ||  {
-        echo_i "dlopen() not supported - skipping filter-aaaa test"
-        exit 255
-}
-exit 0

util/copyrights

@@ -325,7 +325,6 @@
 ./bin/tests/system/dlzexternal/clean.sh		SH	2010,2012,2014,2015,2016,2018,2019,2020
 ./bin/tests/system/dlzexternal/driver/driver.c	C	2011,2012,2013,2014,2015,2016,2017,2018,2019,2020
 ./bin/tests/system/dlzexternal/driver/driver.h	C	2011,2016,2018,2019,2020
-./bin/tests/system/dlzexternal/prereq.sh	SH	2010,2011,2012,2014,2016,2018,2019,2020
 ./bin/tests/system/dlzexternal/setup.sh		SH	2010,2012,2014,2016,2017,2018,2019,2020
 ./bin/tests/system/dlzexternal/tests.sh		SH	2010,2011,2012,2013,2014,2015,2016,2018,2019,2020
 ./bin/tests/system/dns64/clean.sh		SH	2010,2012,2014,2015,2016,2018,2019,2020
@@ -400,7 +399,6 @@
 ./bin/tests/system/dyndb/driver/util.h		X	2015,2018,2019,2020
 ./bin/tests/system/dyndb/driver/zone.c		X	2015,2018,2019,2020
 ./bin/tests/system/dyndb/driver/zone.h		X	2015,2018,2019,2020
-./bin/tests/system/dyndb/prereq.sh		SH	2015,2016,2018,2019,2020
 ./bin/tests/system/dyndb/setup.sh		SH	2018,2019,2020
 ./bin/tests/system/dyndb/tests.sh		SH	2015,2016,2018,2019,2020
 ./bin/tests/system/ecdsa/clean.sh		SH	2012,2014,2016,2018,2019,2020
@@ -436,7 +434,6 @@
 ./bin/tests/system/filter-aaaa/clean.sh		SH	2010,2012,2014,2016,2018,2019,2020
 ./bin/tests/system/filter-aaaa/ns1/sign.sh	SH	2010,2012,2014,2016,2018,2019,2020
 ./bin/tests/system/filter-aaaa/ns4/sign.sh	SH	2010,2012,2014,2016,2018,2019,2020
-./bin/tests/system/filter-aaaa/prereq.sh	SH	2018,2019,2020
 ./bin/tests/system/filter-aaaa/setup.sh		SH	2010,2012,2014,2016,2017,2018,2019,2020
 ./bin/tests/system/filter-aaaa/tests.sh		SH	2010,2012,2015,2016,2018,2019,2020
 ./bin/tests/system/formerr/clean.sh		SH	2013,2014,2015,2016,2018,2019,2020