What are css files prefixed with "REMOVE"?

In visual studio 2013 I got a web project. It uses less files, which I'm learning at the moment. But I can't figure out what the files named with a prefix "REMOVE *.css" are, and what they are used for. Anyone who knows?

For example. I got "REMOVE bootstrap.css" there. It's not referenced anywhere. It contains the complete contents of the real "bootstrap.css". Is it perhaps used for some pre-process less compiler step or some other magic?