How do you unstar a level in Super Mario Maker?

There seems to be no way to unstar a level.

Some anecdotal experiences: 1, 2

There is, however, a way to comment without starring a stage.

1. Play (and possibly clear?) the course
2. Go to Course World
3. Press -
4. Select Played Courses
5. Select View Comments on the course you want Comment in the Miiverse area.

Source