Remove unused Campaign model

The only way to use campaigns is to manually insert them in the
database, which IMHO isn't very practical.

We're going to change every piece of code that generates an Ahoy event
and, in this case, the easiest way to change the Campaing model so it
doesn't use Ahoy events is to simply remove it.

Note we're keeping the database tables until we release a new version,
just in case some Consul Democracy installations are using them. We'll
inform in the release notes that we'll remove the campaigns table after
the release, so existing installations using the `campaigns` table can
move the data somewhere else before we remove the table.

app/controllers/application_controller.rb

@@ -11,7 +11,6 @@ class ApplicationController < ActionController::Base
 
   before_action :ensure_signup_complete
   around_action :switch_locale
-  before_action :track_email_campaign
   before_action :set_return_url
 
   check_authorization unless: :devise_controller?
@@ -91,13 +90,6 @@ class ApplicationController < ActionController::Base
       end
     end
 
-    def track_email_campaign
-      if params[:track_id]
-        campaign = Campaign.find_by(track_id: params[:track_id])
-        ahoy.track campaign.name if campaign.present?
-      end
-    end
-
     def set_return_url
       if request.get? && !devise_controller? && is_navigational_format?
         store_location_for(:user, request.fullpath)

app/models/campaign.rb

@@ -1,2 +0,0 @@
-class Campaign < ApplicationRecord
-end

spec/factories/analytics.rb

@@ -9,9 +9,4 @@ FactoryBot.define do
     id { SecureRandom.uuid }
     started_at { DateTime.current }
   end
-
-  factory :campaign do
-    sequence(:name) { |n| "Campaign #{n}" }
-    sequence(:track_id, &:to_s)
-  end
 end

spec/system/admin/stats_spec.rb

@@ -152,19 +152,21 @@ describe "Stats", :admin do
 
   context "graphs" do
     scenario "event graphs", :with_frozen_time do
-      campaign = create(:campaign)
+      visit new_debate_path
+      fill_in_new_debate_title with: "A title for a debate"
+      fill_in_ckeditor "Initial debate text", with: "This is very important because..."
+      check "debate_terms_of_service"
+      click_button "Start a debate"
 
-      visit root_path(track_id: campaign.track_id)
-
-      expect(page).to have_content "Sign out"
+      expect(page).to have_content "Debate created successfully."
 
       visit admin_stats_path
 
       within("#stats") do
-        click_link campaign.name
+        click_link "Debates"
       end
 
-      expect(page).to have_content "#{campaign.name} (1)"
+      expect(page).to have_content "Debates (1)"
 
       within("#graph") do
         expect(page).to have_content Date.current.strftime("%Y-%m-%d")

spec/system/campaigns_spec.rb

@@ -1,37 +0,0 @@
-require "rails_helper"
-
-describe "Email campaigns", :admin do
-  let!(:campaign1) { create(:campaign) }
-  let!(:campaign2) { create(:campaign) }
-
-  scenario "Track email templates" do
-    3.times { visit root_path(track_id: campaign1.track_id) }
-    5.times { visit root_path(track_id: campaign2.track_id) }
-
-    visit admin_stats_path
-    click_link campaign1.name
-
-    expect(page).to have_content "#{campaign1.name} (3)"
-
-    click_link "Go back"
-    click_link campaign2.name
-
-    expect(page).to have_content "#{campaign2.name} (5)"
-  end
-
-  scenario "Do not track erroneous track_ids" do
-    invalid_id = Campaign.last.id + 1
-
-    visit root_path(track_id: campaign1.track_id)
-    visit root_path(track_id: invalid_id)
-
-    visit admin_stats_path
-
-    expect(page).to have_content campaign1.name
-    expect(page).not_to have_content campaign2.name
-
-    click_link campaign1.name
-
-    expect(page).to have_content "#{campaign1.name} (1)"
-  end
-end