One dictionary (AHD4) defines "censor" as:
1. A person authorized to examine books, films, or other material and to remove or suppress what is considered morally, politically, or otherwise objectionable. 2. An official, as in the armed forces, who examines personal mail and official dispatches to remove information considered secret or a risk to security. 3. One that condemns or censures. 4. One of two officials in ancient Rome responsible for taking the public census and supervising public behavior and morals. 5. Psychology The agent in the unconscious that is responsible for censorship.
and "censorship" as
1. The act, process, or practice of censoring. 2. The office or authority of a Roman censor. 3. Psychology Prevention of disturbing or painful thoughts or feelings from reaching consciousness except in a disguised form.
In both cases, "censorship" carries the implication that there is some clearly identifiable _authority_, usually a specific _office_ and sometimes a single official; e.g. the Lord Chamberlain or the Hays Office or the NBC Standards and Practices office or the New England Watch and Ward society or or the Congregation of the Doctrine of the Faith or the MPAA Ratings Board.
I think the use of the term "self-censorship" muddies the waters. It's NOT the same thing.