you can not remove uncategorized normally as long as the uncategorized still in default wordpress category. To remove uncategorized in wordpress cms, first you have to change default category from uncategorized to another.
how to remove uncategorized in wordpress
1. Open menu Setting, click Writing
2. Click dropdown, and change Uncategory to another.
3. Change uncategory. Example to VPS category
4. Click Save
5. Open Posts Menu, click Category Category
6. Choose (check) Uncategory, click delete in bulk action and click apply
You just removed uncategory.