Easier than you think :)
In admin/general there is a Question classification combobox. If you still want categories then just select that option. Otherwise, go for None.
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.