Remove FF custom_preloader_for_deployments

Changelog: changed

app/serializers/environment_serializer.rb

@@ -52,17 +52,13 @@ class EnvironmentSerializer < BaseSerializer
   end
 
   def batch_load(resource)
-    if ::Feature.enabled?(:custom_preloader_for_deployments, default_enabled: :yaml)
-      resource = resource.preload(environment_associations.except(:last_deployment, :upcoming_deployment))
+    resource = resource.preload(environment_associations.except(:last_deployment, :upcoming_deployment))
 
-      Preloaders::Environments::DeploymentPreloader.new(resource)
-        .execute_with_union(:last_deployment, deployment_associations)
+    Preloaders::Environments::DeploymentPreloader.new(resource)
+      .execute_with_union(:last_deployment, deployment_associations)
 
-      Preloaders::Environments::DeploymentPreloader.new(resource)
-        .execute_with_union(:upcoming_deployment, deployment_associations)
-    else
-      resource = resource.preload(environment_associations)
-    end
+    Preloaders::Environments::DeploymentPreloader.new(resource)
+      .execute_with_union(:upcoming_deployment, deployment_associations)
 
     resource.all.to_a.tap do |environments|
       environments.each do |environment|

config/feature_flags/development/custom_preloader_for_deployments.yml

----
-name: custom_preloader_for_deployments
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/75767
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/348289
-milestone: '14.7'
-type: development
-group: group::release
-default_enabled: false

spec/serializers/environment_serializer_spec.rb

@@ -204,21 +204,6 @@ RSpec.describe EnvironmentSerializer do
 
       json
     end
-
-    # Including for test coverage pipeline failure, remove along with feature flag.
-    context 'when custom preload feature is disabled' do
-      before do
-        Feature.disable(:custom_preloader_for_deployments)
-      end
-
-      it 'avoids N+1 database queries' do
-        control_count = ActiveRecord::QueryRecorder.new { json }.count
-
-        create_environment_with_associations(project)
-
-        expect { json }.not_to exceed_query_limit(control_count)
-      end
-    end
   end
 
   def create_environment_with_associations(project)