Anne Frank's diary is regarded as a beautiful work of literature because of its true-to-life depiction of a girl growing up. Censoring parts of her writing is entirely unfair because, in doing so, those censoring the parts are cutting bits and pieces of truth out of the work that helped to make it so impacting.
There were a lot of other things that Anne Frank talked about that would have been overshadowed if this part had been left in the book. There is no way that her diary would have been read as widespread as it was today if those things had been left in the book. Kids read that book.
This is not just an uncomfortable truth. This book is read in school by many children. At the age children are reading this, this description would not be appropriate. It is an incredibly important book for children to read. However, this section of the book would probably not be appropriate for them to read.
Anne Frank wrote in her diary because she thought it was for her own self. She was revealing her deepest and most private thoughts and feelings, not realizing that others may be reading it in mass numbers some day. I think that censoring the diary helps to protect a bit of her privacy while still getting the point across, showing what she went through in her life.