Does not prevent deletion if the user goes directly to the correct URL

Problem/Motivation

While the "delete" link is not shown for protected taxonomies, If a user goes directly to the URL to delete a protected taxonomy, this module does not prevent them from deleting it.

Steps to reproduce

1. Protect a taxonomy with a machine name of "important_vocabulary".
2. Go to an URL like this: https://example.com/admin/structure/taxonomy/manage/important_vocabulary...
3. Confirm deletion.

Taxonomy is deleted.

Proposed resolution

Prevent access to the route to delete protected taxonomies.