Remove github_import_pull_request_reviews feature flag

Remove Feature flag introduced in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/48632. This
feature is being used since then without any known bugs.

Related to:
- https://gitlab.com/gitlab-org/gitlab/-/issues/289153
- https://gitlab.com/gitlab-org/gitlab/-/merge_requests/48632

app/workers/gitlab/github_import/stage/import_pull_requests_reviews_worker.rb

@@ -11,18 +11,11 @@ module Gitlab
         # client - An instance of Gitlab::GithubImport::Client.
         # project - An instance of Project.
         def import(client, project)
-          waiter =
-            if Feature.enabled?(:github_import_pull_request_reviews, project, default_enabled: true)
-              waiter = Importer::PullRequestsReviewsImporter
-                .new(project, client)
-                .execute
+          waiter = Importer::PullRequestsReviewsImporter
+            .new(project, client)
+            .execute
 
-              project.import_state.refresh_jid_expiration
-
-              waiter
-            else
-              JobWaiter.new
-            end
+          project.import_state.refresh_jid_expiration
 
           AdvanceStageWorker.perform_async(
             project.id,

config/feature_flags/development/github_import_pull_request_reviews.yml

----
-name: github_import_pull_request_reviews
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/48632
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/289153
-milestone: '13.7'
-type: development
-group: group::import
-default_enabled: true

spec/workers/gitlab/github_import/stage/import_pull_requests_reviews_worker_spec.rb

@@ -9,23 +9,7 @@ RSpec.describe Gitlab::GithubImport::Stage::ImportPullRequestsReviewsWorker do
   let(:client) { double(:client) }
 
   describe '#import' do
-    it 'does not import with the feature disabled' do
-      stub_feature_flags(github_import_pull_request_reviews: false)
-
-      expect(Gitlab::JobWaiter)
-        .to receive(:new)
-        .and_return(double(key: '123', jobs_remaining: 0))
-
-      expect(Gitlab::GithubImport::AdvanceStageWorker)
-        .to receive(:perform_async)
-        .with(project.id, { '123' => 0 }, :issues_and_diff_notes)
-
-      worker.import(client, project)
-    end
-
     it 'imports all the pull request reviews' do
-      stub_feature_flags(github_import_pull_request_reviews: true)
-
       importer = double(:importer)
 
       waiter = Gitlab::JobWaiter.new(2, '123')