No, it's not... Otherwise 'government censorship' would be redundant. I just checked the top 5 google results for "censorship definition" [0] [1] [2] [3] [4] and NONE of them limited it to government only. I mean, the first sentence of the Wikipedia article even mentions corporate censorship specifically: "...as determined by a government or private institution, for example, corporate censorship."

0: https://www.merriam-webster.com/dictionary/censorship 1: https://en.oxforddictionaries.com/definition/censorship 2: https://en.wikipedia.org/wiki/Censorship 3: https://www.vocabulary.com/dictionary/censorship 4: https://www.aclu.org/other/what-censorship