Remove rate_limit_user_sign_up_endpoint feature flag

Enforce rate limit of 20 calls per minute
per IP address on /users/sign_up endpoint

Changelog: added

app/controllers/registrations_controller.rb

@@ -15,7 +15,7 @@ class RegistrationsController < Devise::RegistrationsController
   before_action :load_recaptcha, only: :new
   before_action :set_invite_params, only: :new
   before_action only: [:create] do
-    check_rate_limit!(:user_sign_up, scope: request.ip) if Feature.enabled?(:rate_limit_user_sign_up_endpoint, default_enabled: :yaml)
+    check_rate_limit!(:user_sign_up, scope: request.ip)
   end
 
   before_action only: [:new] do

config/feature_flags/development/rate_limit_user_sign_up_endpoint.yml

----
-name: rate_limit_user_sign_up_endpoint
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/77835
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/349843
-milestone: '14.7'
-type: development
-group: group::optimize
-default_enabled: false