On the top bar of the My Courses list, click the "pencil" icon. The resulting window lets you select which courses you want to see on that list. If you uncheck a course's box under the "Display Course" column, also be sure to uncheck its box under the "Display Announcements" column. Click Submit to record your changes.
You can always return to the same page to restore your quick access to any courses in which you are enrolled.