Remove seat_link_enabled from ApplicationSettings db table

Prior to this change, the column seat_link_enabled in
ApplicationSettings was ignored in the previous milestone. Now, the
column can be removed from the database.

Changelog: removed
MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/66534

db/post_migrate/20210721122840_remove_seat_link_enabled_from_application_settings.rb

+# frozen_string_literal: true
+
+class RemoveSeatLinkEnabledFromApplicationSettings < ActiveRecord::Migration[6.1]
+  def up
+    remove_column :application_settings, :seat_link_enabled
+  end
+
+  def down
+    add_column :application_settings, :seat_link_enabled, :boolean, null: false, default: true
+  end
+end

db/schema_migrations/20210721122840

+483ef6f8ef379f39ecff32853c777c12c59d2858f061879c375ff6d429396167
\ No newline at end of file

db/structure.sql

@@ -9540,7 +9540,6 @@ CREATE TABLE application_settings (
     email_restrictions_enabled boolean DEFAULT false NOT NULL,
     email_restrictions text,
     npm_package_requests_forwarding boolean DEFAULT true NOT NULL,
-    seat_link_enabled boolean DEFAULT true NOT NULL,
     container_expiration_policies_enable_historic_entries boolean DEFAULT false NOT NULL,
     issues_create_limit integer DEFAULT 0 NOT NULL,
     push_rule_id bigint,