I have a very simple question, how do I remove a menu from a WordPress site? Is there a plugin out there that can handle this or do I have to go into my theme's code and remove something from there?
In your admin panel, go to Appearance > Menus > Manage Locations
There you make sure that none of the theme locations have a menu assigned.
Alternatively, you can modify your theme.
If you want to do that, search for calls to wp_nav_menu.
If you take theme twentyfourteen, you have 2 files: header.php and sidebar.php
in header.php the portion to update looks like
Note: if you want to modify a theme, create a child theme as your modifications would be overwritten when you update the theme.