Removing a class is probably the same as removing a race, I did it a while back, but I don't really remember
I would say delete the class from charclass.dbc, remove it from charbaseinfo.dbc and remove it from the chatactercreate.lua an xml documents, sorry if I got names wrong, writing from phone
Also I would delete anything character creation related in the db though I'm not sure that's necessary
Ah just thought of something if that doesn't work you may need to delete the class from SharedDefines.h