Remove the jira_connect_installation_update flag

The flag was added in 19722d41.

https://gitlab.com/gitlab-org/gitlab/-/issues/356083

Changelog: changed

app/controllers/jira_connect/events_controller.rb

@@ -7,10 +7,6 @@ class JiraConnect::EventsController < JiraConnect::ApplicationController
   before_action :verify_asymmetric_atlassian_jwt!
 
   def installed
-    unless Feature.enabled?(:jira_connect_installation_update, default_enabled: :yaml)
-      return head :ok if current_jira_installation
-    end
-
     success = current_jira_installation ? update_installation : create_installation
 
     if success

config/feature_flags/development/jira_connect_installation_update.yml

----
-name: jira_connect_installation_update
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/83038
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/356083
-milestone: '14.9'
-type: development
-group: group::integrations
-default_enabled: false

spec/controllers/jira_connect/events_controller_spec.rb

@@ -114,17 +114,6 @@ RSpec.describe JiraConnect::EventsController do
             base_url: base_url
           )
         end
-
-        context 'when the `jira_connect_installation_update` feature flag is disabled' do
-          before do
-            stub_feature_flags(jira_connect_installation_update: false)
-          end
-
-          it 'does not update the installation', :aggregate_failures do
-            expect { subject }.not_to change { installation.reload.attributes }
-            expect(response).to have_gitlab_http_status(:ok)
-          end
-        end
       end
 
       context 'when the new base_url is invalid' do