siproxd: update libltdl handling

Remove LIBLTDL from the Makefile as well as a patch related to LTDL.
Both have in common that they accomplish absolutely nothing.

Also explicitly disable the use of the internal libltdl.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>

net/siproxd/Makefile

@@ -1,5 +1,5 @@
 #
-# Copyright (C) 2014-2017 OpenWrt.org
+# Copyright (C) 2014-2018 OpenWrt.org
 #
 # This is free software, licensed under the GNU General Public License v2.
 # See /LICENSE for more information.
@@ -48,11 +48,11 @@ endef
 
 CONFIGURE_ARGS+= \
 	--with-libosip-prefix="$(STAGING_DIR)/usr" \
+	--disable-ltdl-convenience \
 	--disable-doc
 
 MAKE_FLAGS+= \
-	SUBDIRS="src scripts contrib" \
+	SUBDIRS="src scripts contrib"
-	LIBLTDL="$(STAGING_DIR)/usr/lib/libltdl.la" \
 
 define Package/siproxd/install
 	$(INSTALL_DIR) $(1)/usr/sbin

net/siproxd/patches/010-fix-bogus-libltdl-dependency.patch

@@ -1,26 +0,0 @@
---- a/src/Makefile.am
-+++ b/src/Makefile.am
-@@ -103,8 +103,8 @@
- #  else Cygwin goes beserk when building...)
- #
- sbin_PROGRAMS = siproxd
--siproxd_LDFLAGS=-export-dynamic
--siproxd_LDADD = $(LIBLTDL) $(DLOPENPLUGINS)
-+siproxd_LDFLAGS=-export-dynamic -lltdl
-+siproxd_LDADD = $(DLOPENPLUGINS)
- siproxd_SOURCES = siproxd.c proxy.c register.c sock.c utils.c \
- 		  sip_utils.c sip_layer.c log.c readconf.c rtpproxy.c \
- 		  rtpproxy_relay.c accessctl.c route_processing.c \
---- a/src/Makefile.in
-+++ b/src/Makefile.in
-@@ -377,8 +377,8 @@
- #
- plugin_fix_fbox_anoncall_la_SOURCES = plugin_fix_fbox_anoncall.c
- plugin_fix_fbox_anoncall_la_LDFLAGS = -module -avoid-version -shrext '.so'
--siproxd_LDFLAGS = -export-dynamic
--siproxd_LDADD = $(LIBLTDL) $(DLOPENPLUGINS)
-+siproxd_LDFLAGS = -export-dynamic -lltdl
-+siproxd_LDADD = $(DLOPENPLUGINS)
- siproxd_SOURCES = siproxd.c proxy.c register.c sock.c utils.c \
- 		  sip_utils.c sip_layer.c log.c readconf.c rtpproxy.c \
- 		  rtpproxy_relay.c accessctl.c route_processing.c \