tests: clean up test-rollback.t

The last comment is on the last file line and is useless, seems
like it was introduced in 8fdc11fec6ae during unification.

tests/test-rollback.t

@@ -72,8 +72,9 rollback by pretxncommit saves commit me
 
   $ cat .hg/last-message.txt ; echo
   precious commit message
-  $ echo '% same thing, but run $EDITOR'
-  % same thing, but run $EDITOR
+
+same thing, but run $EDITOR
+
   $ cat > editor << '__EOF__'
   > #!/bin/sh
   > echo "another precious commit message" > "$1"
@@ -88,5 +89,3 rollback by pretxncommit saves commit me
   $ cat .hg/last-message.txt
   another precious commit message
 
-.hg/last-message.txt:
-