Change name to elwig-rest-backend

pkg/prerm

@@ -1,5 +1,5 @@
 #!/bin/sh
 set -e
 if [ -d /run/systemd/system ] && [ "$1" = remove ]; then
-  deb-systemd-invoke stop 'elwig-backend.service' >/dev/null || true
+  deb-systemd-invoke stop 'elwig-rest-backend.service' >/dev/null || true
 fi