add delete-storage-file function in nera package.

src/nera.lisp

@@ -264,3 +264,10 @@ slug is updated based on `NEW-FILE-NAME'."
       (setf (files::name-of file-to-rename) new-file-name
 	    (files::slug-of file-to-rename) (utils:slugify new-file-name))
       (mito:save-dao file-to-rename))))
+
+(defun delete-storage-file (&key name slug)
+  "Delete `STORAGE-FILE' from database."
+  (with-connection (db)
+    (if (null slug)
+	(mito:delete-by-values 'files:storage-file :name name)
+	(mito:delete-by-values 'files:storage-file :slug slug))))