Haven't tried removing nano ever but hate it with a passion for one simple reason.

If none of the EDITOR/VISUAL/etc. variables are set when you invoke 'visudo' a f*king nano appears.

Like god dammit it i assume vi in that name comes from vi as even the manpage has 'vi' among 'see also'. This is akin to launching firefox and some random application popping up - its the ultimate troll and i salute your graybeards for solving the problem at the core!