DULUTH, Mn (KDAL) - Students wrapped up classes this week for the final time at Central High School in Duluth.   As part of the School District's Long Range Facilities Plan, Central closes and Duluth will have just two high schools beginning in September.   Mayor Don Ness, a Central alumnus and the fourth generation of his family to graduate from Central, has declared Thursday as "Duluth Central Day" and encouraged all alumni and friends to wear the school colors of red and white.  Ness says its a sad day and the end of an era but it is not the end to the history of the school.