Don't log Action Cable to STDOUT in development

Logging Action Cable to STDOUT caused the development log to see double
messages like this:

```
Started GET "/" for ::1 at 2015-12-17 15:21:34 -0500
Started GET "/" for ::1 at 2015-12-17 15:21:34 -0500
Processing by Rails::WelcomeController#index as HTML
Processing by Rails::WelcomeController#index as HTML
Rendered /welcome/index.html.erb (0.0ms)
Rendered /welcome/index.html.erb (0.0ms)
Completed 200 OK in 3ms (Views: 1.3ms | ActiveRecord: 0.0ms)
Completed 200 OK in 3ms (Views: 1.3ms | ActiveRecord: 0.0ms)
```

Now that Action Cable is part of Rails it doesn't need it's own logger
and will log to STDOUT via the local dev server here:
https://github.com/rails/rails/blob/master/railties/lib/rails/commands/server.rb

actioncable/lib/action_cable/process/logging.rb

@@ -8,5 +8,3 @@
 end
 
 Celluloid.logger = ActionCable.server.logger
-
-ActionCable.server.config.log_to_stdout if Rails.env.development?
\ No newline at end of file

actioncable/lib/action_cable/server/configuration.rb

@@ -20,14 +20,6 @@ def initialize
         @disable_request_forgery_protection = false
       end
 
-      def log_to_stdout
-        console = ActiveSupport::Logger.new($stdout)
-        console.formatter = @logger.formatter
-        console.level = @logger.level
-
-        @logger.extend(ActiveSupport::Logger.broadcast(console))
-      end
-
       def channel_paths
         @channels ||= Dir["#{channels_path}/**/*_channel.rb"]
       end