Revert "Set ID field to 0"

This reverts commit 0afe50e.

lib/Zonemaster/Engine/Nameserver.pm

@@ -528,13 +528,6 @@ sub save {
     open my $fh, '>', $filename or die "Cache save failed: $!";
     foreach my $name ( sort keys %object_cache ) {
         foreach my $addr ( sort keys %{ $object_cache{$name} } ) {
-
-            # set ID field of packets to 0
-            my %data = %{ $object_cache{$name}{$addr}->cache->data };
-            foreach my $key ( keys %data ){
-                $data{$key}->packet->id( 0 ) if defined( $data{$key} );
-            }
-
             say $fh "$name $addr " . $json->encode( $object_cache{$name}{$addr}->cache->data );
         }
     }