src:iptables: drop /sbin -> /usr/sbin compat symlinks

Debian Buster included them, it should be enough to have a Debian release as
transition period. So drop them, no longer required.

The code in prerm is left so we can clean old symlinks when deleting the
package.

While at it, introduce a new NEWS entry to explain this and other important
changes in this release.
Signed-off-by: Arturo Borrero Gonzalez <arturo@debian.org>

debian/NEWS

+iptables (1.8.4-1) unstable; urgency=medium
+
+    All the iptables binaries have been moved away from /sbin to /usr/sbin.
+    Compatibility symlinks were provided during the Buster release, but they
+    have been dropped now.
+    Please make sure your scripts aren't using hardcoded binary paths.
+    .
+    Also, please note that iptables is no longer Priority: important. This
+    means it is not installed by default in every system. It has been replaced
+    by nftables.
+
+ -- Arturo Borrero Gonzalez <arturo@debian.org>  Wed,  04 Dec 2019 11:49:00 +0200
+
 iptables (1.8.1-2) unstable; urgency=medium
 
     All the iptables binaries have been moved away from /sbin to /usr/sbin.

debian/iptables.postinst

@@ -2,22 +2,6 @@
 
 set -e
 
-# compat symlinks for /sbin -> /usr/sbin move, to be dropped in buster+1
-if [ "$1" = "configure" ] ; then
-	LIST="/sbin/iptables
-	      /sbin/iptables-save
-	      /sbin/iptables-restore
-	      /sbin/ip6tables
-              /sbin/ip6tables-save
-              /sbin/ip6tables-restore"
-
-	for i in $LIST ; do
-		if [ ! -e "$i" ] ; then
-			ln -sf /usr$i $i
-		fi
-	done
-fi
-
 if [ "$1" = "configure" ] || [ "$1" = "abort-upgrade" ]; then
 	update-alternatives \
 	  --install /usr/sbin/iptables iptables /usr/sbin/iptables-legacy 10 \

debian/iptables.prerm

@@ -11,7 +11,9 @@ if [ "$1" != "upgrade" ]; then
     update-alternatives --remove ebtables /usr/sbin/ebtables-nft
 fi
 
-# compat symlinks for /sbin -> /usr/sbin move, to be dropped in buster+1
+# remove compat symlinks for /sbin -> /usr/sbin move
+# This piece of code can be dropped eventually, when we are confident user
+# systems are left in a consistent state.
 if [ "$1" = "remove" ] ; then
 	LIST="/sbin/iptables
 	     /sbin/iptables-save