Fix the sed script that Tobias had right in the first place and I mangled in the previous upload.

debian/changelog

@@ -1,3 +1,10 @@
+livecd-rootfs (2.578) UNRELEASED; urgency=medium
+
+  * Fix the sed script that Tobias had right in the first place and I
+    mangled in the previous upload.
+
+ -- Steve Langasek <steve.langasek@ubuntu.com>  Sat, 13 Apr 2019 02:12:51 -0700
+
 livecd-rootfs (2.577) disco; urgency=medium
 
   [ Tobias Koch ]

live-build/functions

@@ -448,7 +448,7 @@ _snap_post_process() {
                 # Remove snap, assertions and entry in seed.yaml
                 rm -f ${snaps_dir}/snapd_[0-9]*.snap
                 rm -f ${assertions_dir}/snapd_[0-9]*.assert
-                sed -i -e'/name: snapd/,+2d' $seed_yaml
+                sed -i -e'N;/name: snapd/,+2d' $seed_yaml
             fi
             ;;
         *)