Remove `error_tracking` feature flag

We introduced the feature flag `error_tracking` to test the Sentry MVC
safely.

After the successful test, we remove it again.

app/assets/javascripts/error_tracking/index.js

@@ -4,10 +4,6 @@ import store from './store';
 import ErrorTrackingList from './components/error_tracking_list.vue';
 
 export default () => {
-  if (!gon.features.errorTracking) {
-    return;
-  }
-
   // eslint-disable-next-line no-new
   new Vue({
     el: '#js-error_tracking',

app/controllers/projects/error_tracking_controller.rb

 # frozen_string_literal: true
 
 class Projects::ErrorTrackingController < Projects::ApplicationController
-  before_action :check_feature_flag!
   before_action :authorize_read_sentry_issue!
-  before_action :push_feature_flag_to_frontend
 
   POLLING_INTERVAL = 10_000
 
@@ -43,12 +41,4 @@ class Projects::ErrorTrackingController < Projects::ApplicationController
       .new(project: project, user: current_user)
       .represent(errors)
   end
-
-  def check_feature_flag!
-    render_404 unless Feature.enabled?(:error_tracking, project)
-  end
-
-  def push_feature_flag_to_frontend
-    push_frontend_feature_flag(:error_tracking, current_user)
-  end
 end

app/helpers/projects_helper.rb

@@ -285,7 +285,7 @@ module ProjectsHelper
 
   # overridden in EE
   def settings_operations_available?
-    Feature.enabled?(:error_tracking, @project) && can?(current_user, :read_environment, @project)
+    can?(current_user, :read_environment, @project)
   end
 
   private

app/views/layouts/nav/sidebar/_project.html.haml

@@ -227,7 +227,7 @@
                   %span
                     = _('Environments')
 
-            - if project_nav_tab?(:error_tracking) && Feature.enabled?(:error_tracking, @project)
+            - if project_nav_tab?(:error_tracking)
               = nav_link(controller: :error_tracking) do
                 = link_to project_error_tracking_index_path(@project), title: _('Error Tracking'), class: 'shortcuts-tracking qa-operations-tracking-link' do
                   %span

app/views/projects/settings/operations/_error_tracking.html.haml

-- return unless Feature.enabled?(:error_tracking, @project) && can?(current_user, :read_environment, @project)
+- return unless can?(current_user, :read_environment, @project)
 
 - setting = error_tracking_setting
 

spec/controllers/projects/error_tracking_controller_spec.rb

@@ -20,18 +20,6 @@ describe Projects::ErrorTrackingController do
         expect(response).to render_template(:index)
       end
 
-      context 'with feature flag disabled' do
-        before do
-          stub_feature_flags(error_tracking: false)
-        end
-
-        it 'returns 404' do
-          get :index, params: project_params
-
-          expect(response).to have_gitlab_http_status(:not_found)
-        end
-      end
-
       context 'with insufficient permissions' do
         before do
           project.add_guest(user)

spec/controllers/projects/settings/operations_controller_spec.rb

@@ -41,18 +41,6 @@ describe Projects::Settings::OperationsController do
         end
       end
 
-      context 'with feature flag disabled' do
-        before do
-          stub_feature_flags(error_tracking: false)
-        end
-
-        it 'renders 404' do
-          get :show, params: project_params(project)
-
-          expect(response).to have_gitlab_http_status(:not_found)
-        end
-      end
-
       context 'with insufficient permissions' do
         before do
           project.add_reporter(user)
@@ -121,18 +109,6 @@ describe Projects::Settings::OperationsController do
         end
       end
 
-      context 'with feature flag disabled' do
-        before do
-          stub_feature_flags(error_tracking: false)
-        end
-
-        it 'renders 404' do
-          patch :update, params: project_params(project)
-
-          expect(response).to have_gitlab_http_status(:not_found)
-        end
-      end
-
       context 'with insufficient permissions' do
         before do
           project.add_reporter(user)

spec/features/projects/settings/operations_settings_spec.rb

@@ -8,13 +8,11 @@ describe 'Projects > Settings > For a forked project', :js do
   let(:role) { :maintainer }
 
   before do
-    stub_feature_flags(error_tracking: true)
     sign_in(user)
     project.add_role(user, role)
   end
 
   describe 'Sidebar > Operations' do
-    context 'when sidebar feature flag enabled' do
     it 'renders the settings link in the sidebar' do
       visit project_path(project)
       wait_for_requests
@@ -22,18 +20,4 @@ describe 'Projects > Settings > For a forked project', :js do
       expect(page).to have_selector('a[title="Operations"]', visible: false)
     end
   end
-
-    context 'when sidebar feature flag disabled' do
-      before do
-        stub_feature_flags(error_tracking: false)
-      end
-
-      it 'does not render the settings link in the sidebar' do
-        visit project_path(project)
-        wait_for_requests
-
-        expect(page).not_to have_selector('a[title="Operations"]', visible: false)
-      end
-    end
-  end
 end

spec/views/projects/settings/operations/show.html.haml_spec.rb

@@ -13,8 +13,6 @@ describe 'projects/settings/operations/show' do
 
   describe 'Operations > Error Tracking' do
     before do
-      stub_feature_flags(error_tracking: true)
-
       project.add_reporter(user)
 
       allow(view).to receive(:error_tracking_setting)