Purge all menu links from Main Menu

I just started work on migrating the Medical Library website to the YaleSites 2016 Standard theme. 

One large problem i’ve already discovered is that it looks like we will need to rebuild our existing navigation menu in the Main Menu (http://dev.library.medicine.yale.edu/admin/structure/menu/manage/main-menu)  if we want a responsive menu.  Is this correct?  

If that’s the case, we will somehow need to clear out the garbage existing data that is already in this menu - basically every page in our site is listed and it is not practical to go through and delete each one manually. I am guessing this will have to be done through a mysql operation.  

Let’s schedule a time to chat by phone.  Josue and i are already supposed to chat so i will ping him with this in a moment.