Explicitly disable the unused ActionCable Rails feature

Just for consistency with the other features we're not using, we turn
off ActionCable when loading the app. I just removed
`config/cable.yml`, so I figure, let's not load a feature without the
config file it expects! (even though that didn't seem to bother it)

config/application.rb

@@ -9,11 +9,11 @@ require "rails"
 # Disabled:
 # - active_storage/engine
 # - active_job/railtie
+# - action_cable/engine
 # - action_mailbox/engine
 # - action_text/engine
 %w(
   active_record/railtie
-  action_cable/engine
   action_controller/railtie
   action_view/railtie
   action_mailer/railtie

config/cable.yml

@@ -1,10 +0,0 @@
-development:
-  adapter: async
-
-test:
-  adapter: test
-
-production:
-  adapter: redis
-  url: <%= ENV.fetch("REDIS_URL") { "redis://localhost:6379/1" } %>
-  channel_prefix: openneo_impress_items_production

config/storage.yml

@@ -1,34 +0,0 @@
-test:
-  service: Disk
-  root: <%= Rails.root.join("tmp/storage") %>
-
-local:
-  service: Disk
-  root: <%= Rails.root.join("storage") %>
-
-# Use rails credentials:edit to set the AWS secrets (as aws:access_key_id|secret_access_key)
-# amazon:
-#   service: S3
-#   access_key_id: <%= Rails.application.credentials.dig(:aws, :access_key_id) %>
-#   secret_access_key: <%= Rails.application.credentials.dig(:aws, :secret_access_key) %>
-#   region: us-east-1
-#   bucket: your_own_bucket
-
-# Remember not to checkin your GCS keyfile to a repository
-# google:
-#   service: GCS
-#   project: your_project
-#   credentials: <%= Rails.root.join("path/to/gcs.keyfile") %>
-#   bucket: your_own_bucket
-
-# Use rails credentials:edit to set the Azure Storage secret (as azure_storage:storage_access_key)
-# microsoft:
-#   service: AzureStorage
-#   storage_account_name: your_account_name
-#   storage_access_key: <%= Rails.application.credentials.dig(:azure_storage, :storage_access_key) %>
-#   container: your_container_name
-
-# mirror:
-#   service: Mirror
-#   primary: local
-#   mirrors: [ amazon, google, microsoft ]