Home > Welcome to Moodle > Gradebook in Moodle > Gradebook: Manual Grades (Grades for things outside of Moodle) > Gradebook: Delete a Manual Grade Item
To remove Moodle activities like Forums, Quizzes or Assignments you will need to set their grade type to None or delete them from the main course page/weekly view of your course.
Steps for doing that are not covered in this article.