def delete(username, realm)
      if has_entry?(username, realm) then
        ir = internal_record(username, realm)
        line_index = ir['line_index']
        @entries.delete(ir['entry'].key)
        @lines[line_index] = nil
        dirty!
      end
      nil
    end
def delete(username, realm)
      if has_entry?(username, realm) then
        ir = internal_record(username, realm)
        line_index = ir['line_index']
        @entries.delete(ir['entry'].key)
        @lines[line_index] = nil
        dirty!
      end
      nil
    end
Public: remove the given username / realm from the file.
 The file is not written to disk until #save! is called.

 username - the username to remove
 realm    - the realm to remove

 Examples

   digest_file.delete("myuser", "myrealm")
   digest_file.save!

 Returns nothing