Remove protected attributes

It was failing in the main apps 'cause of protected attributes.
http://localhost:3001/tematica/tematicas/new
Just a little comment (don't change it), but lists of symbols can be created with `%i{}`:
```ruby
%i(nombre portada_path seccion_publi publicado)
=> [:nombre, :portada_path, :seccion_publi, :publicado]
```