So Calypso is still running fine. Any change you make does end up on your site like it has always done. Ok.
One possible cause is that have you only removed part of what your training developer has added. There is a good chance that he has also added this code at another location that you have not yet removed.
And there is always overriding it with your own extra code marked with the !important escape, but being a professional you of course do not have to use that.
Thanks guys, finally found it.
The little basterd added this class to the bottom of the main.scss file aswell where i never tought to look :)
Also try to clean and rebuild the project directory
Just to be sure, you changed/removed this part in the project root folder > theme > styles > sass and not in deployment > web > styles > sass ?