Use system ldns library

This library is used only by mod_enum and is available on most
platforms.  The version in our tree has many code quality problems
that are generating noise when doing static analysis.  Suffice it to
say we want rid of it as our responsibility.

FS-353

bootstrap.sh

@@ -9,7 +9,7 @@ VERBOSE=false
 BASEDIR=`pwd`;
 LIBDIR=${BASEDIR}/libs;
 SUBDIRS="apr \
-  libzrtp ilbc iksemel js js/nsprpub ldns libdingaling libsndfile sofia-sip \
+  libzrtp ilbc iksemel js js/nsprpub libdingaling libsndfile sofia-sip \
   speex srtp openzap freetdm spandsp libg722_1 portaudio unimrcp tiff-4.0.2 broadvoice silk libcodec2 \
   fs";
 
@@ -427,14 +427,7 @@ bootstrap_libs_pre() {
 
 bootstrap_libs_post() {
   case "$1" in
-    ldns)
-      cd $BASEDIR/libs/ldns
-      if test ! -x install-sh; then
-        ex ${AUTOMAKE:-automake} --add-missing --copy
-        ex rm -rf autom4te*.cache
-        chmod a+x install-sh
-      fi
-      ;;
+    *) return 0;;
   esac
 }