Removes security_ci_lint_authorization code

Changelog: security

config/feature_flags/development/security_ci_lint_authorization.yml

----
-name: security_ci_lint_authorization
-introduced_by_url: https://gitlab.com/gitlab-org/security/gitlab/-/merge_requests/1279
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/326708
-milestone: '14.0'
-type: development
-group: group::pipeline authoring
-default_enabled: false

lib/api/lint.rb

@@ -11,11 +11,7 @@ module API
         optional :include_merged_yaml, type: Boolean, desc: 'Whether or not to include merged CI config yaml in the response'
       end
       post '/lint' do
-        if Feature.enabled?(:security_ci_lint_authorization)
-          unauthorized! if (Gitlab::CurrentSettings.signup_disabled? || Gitlab::CurrentSettings.signup_limited?) && current_user.nil?
-        else
-          unauthorized! if Gitlab::CurrentSettings.signup_disabled? && current_user.nil?
-        end
+        unauthorized! if (Gitlab::CurrentSettings.signup_disabled? || Gitlab::CurrentSettings.signup_limited?) && current_user.nil?
 
         result = Gitlab::Ci::YamlProcessor.new(params[:content], user: current_user).execute