Add and remove taxonomies: Remove categories
To remove a Category you need to perform the following:
    - Use 
TaxonomyManager which is the manager class for taxonomies.
     
    - Query the category as a 
HierarchicalTaxon.
     
    - Call the manager’s 
Delete method.
     
    - Call the manager’s 
SaveChanges method to persist the changes to the database.
     
Use the following code snippet:
The same approach can be used with all flat and hierarchical taxonomies not only for tags and categories.
Use the following code snippet as an example where Cities is a custom Flat Taxonomy that you created: