Remove prevent_retry_of_retried_jobs feature flag

This feature flag prevents already-retried builds from being retried
again. This feature flag:

* shipped in GitLab 14.0:
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/62349

* enabled by defualt in GitLab 14.0:
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/63112

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/331695

Changelog: changed

app/models/ci/build.rb

@@ -466,13 +466,9 @@ module Ci
     end
 
     def retryable?
-      if Feature.enabled?(:prevent_retry_of_retried_jobs, project, default_enabled: :yaml)
-        return false if retried? || archived?
+      return false if retried? || archived?
 
-        success? || failed? || canceled?
-      else
-        !archived? && (success? || failed? || canceled?)
-      end
+      success? || failed? || canceled?
     end
 
     def retries_count

config/feature_flags/development/prevent_retry_of_retried_jobs.yml

----
-name: prevent_retry_of_retried_jobs
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/62349
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/331695
-milestone: '14.0'
-type: development
-group: group::pipeline execution
-default_enabled: true

spec/models/ci/build_spec.rb

@@ -1955,17 +1955,7 @@ RSpec.describe Ci::Build do
             described_class.retry(build, user)
           end
 
-          context 'when prevent_retry_of_retried_jobs feature flag is enabled' do
-            it { is_expected.not_to be_retryable }
-          end
-
-          context 'when prevent_retry_of_retried_jobs feature flag is disabled' do
-            before do
-              stub_feature_flags(prevent_retry_of_retried_jobs: false)
-            end
-
-            it { is_expected.to be_retryable }
-          end
+          it { is_expected.not_to be_retryable }
         end
       end
     end