Skip setting Rails config on actual objects

Brakeman builds up a hash table of Rails configs for an application by converting code like

```ruby
config.this.little.setting = :value
```

into

```ruby
config[:this][:little][:setting] = :value
```

However, this does not work out so well:

```ruby
config.this.little = Setting.new
config.this.little.setting = :value
```

Because `config[:this][:little]` is no longer a hash.

For now, skipping this kind of situation until it is actually needed for a Brakeman check.