Remove project_only from Services, prevent view exception instead

This commit removes changes that created project_only services,
in favour of simply stopping the exception that occurs when
trying to set application-wide settings for generic alerts in
the Admin Area.

app/controllers/admin/services_controller.rb

@@ -7,7 +7,7 @@ class Admin::ServicesController < Admin::ApplicationController
   before_action :service, only: [:edit, :update]
 
   def index
-    @services = services_templates.reject(&:project_only?)
+    @services = services_templates
   end
 
   def edit

app/models/service.rb

@@ -330,11 +330,6 @@ class Service < ApplicationRecord
     false
   end
 
-  # Override for services supported at project level only
-  def project_only?
-    false
-  end
-
   private
 
   def cache_project_has_external_issue_tracker

changelogs/unreleased/remove_alerts_service_from_admin_area_service_templates.yml

----
-title: Exclude project-only services from the admin service templates area
-merge_request: 20938
-author:
-type: fixed

ee/app/models/project_services/alerts_service.rb

@@ -58,10 +58,6 @@ class AlertsService < Service
     super || build_data
   end
 
-  def project_only?
-    true
-  end
-
   private
 
   def prevent_token_assignment

ee/app/views/projects/services/alerts/_help.html.haml

-- return unless @project.alerts_service_available?
+- return unless @project&.alerts_service_available?
 
 .js-alerts-service-settings{ data: { activated: @service.activated?.to_s,
   form_path: project_service_path(@project, @service.to_param),

ee/spec/models/project_services/alerts_service_spec.rb

@@ -106,8 +106,4 @@ describe AlertsService do
       it_behaves_like 'valid token'
     end
   end
-
-  describe '#project_only?' do
-    it { expect(service).to be_project_only }
-  end
 end

spec/controllers/admin/services_controller_spec.rb

@@ -9,15 +9,6 @@ describe Admin::ServicesController do
     sign_in(admin)
   end
 
-  describe 'GET #index' do
-    it 'does not show project_only services' do
-      get :index
-
-      expect(assigns(:services)).not_to include(be_project_only),
-        "expected to exclude project_only services"
-    end
-  end
-
   describe 'GET #edit' do
     let!(:project) { create(:project) }
 

spec/models/service_spec.rb

@@ -399,12 +399,6 @@ describe Service do
     end
   end
 
-  describe '#project_only?' do
-    let(:service) { build_stubbed(:service, template: true) }
-
-    it { expect(service).not_to be_project_only }
-  end
-
   describe '#api_field_names' do
     let(:fake_service) do
       Class.new(Service) do