Chore: Remove dead code related to billing (#935)

- remove subscription model
- remove billing-related code

app/controllers/api/v1/webhooks_controller.rb

@@ -1,18 +1,6 @@
 class Api::V1::WebhooksController < ApplicationController
   skip_before_action :authenticate_user!, raise: false
   skip_before_action :set_current_user
-  skip_before_action :check_subscription
-
-  before_action :login_from_basic_auth, only: [:chargebee]
-  before_action :check_billing_enabled, only: [:chargebee]
-
-  def chargebee
-    chargebee_consumer.consume
-    head :ok
-  rescue StandardError => e
-    Raven.capture_exception(e)
-    head :ok
-  end
 
   def twitter_crc
     render json: { response_token: "sha256=#{twitter_client.generate_crc(params[:crc_token])}" }
@@ -34,16 +22,6 @@ class Api::V1::WebhooksController < ApplicationController
     end
   end
 
-  def login_from_basic_auth
-    authenticate_or_request_with_http_basic do |username, password|
-      username == ENV['CHARGEBEE_WEBHOOK_USERNAME'] && password == ENV['CHARGEBEE_WEBHOOK_PASSWORD']
-    end
-  end
-
-  def chargebee_consumer
-    @chargebee_consumer ||= ::Webhooks::Chargebee.new(params)
-  end
-
   def twitter_consumer
     @twitter_consumer ||= ::Webhooks::Twitter.new(params)
   end