Drop Delayed Project Removal column from Namespaces

Column has been ignored for several releases so it's now safe
to drop it.

Changelog: removed

db/post_migrate/20210923135909_remove_delayed_project_removal_from_namespaces.rb

+# frozen_string_literal: true
+
+class RemoveDelayedProjectRemovalFromNamespaces < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  def up
+    with_lock_retries do
+      remove_column :namespaces, :delayed_project_removal
+    end
+  end
+
+  def down
+    with_lock_retries do
+      add_column :namespaces, :delayed_project_removal, :boolean, default: false, null: false, if_not_exists: true # rubocop:disable Migration/AddColumnsToWideTables
+    end
+
+    add_concurrent_index :namespaces, :id, name: 'tmp_idx_on_namespaces_delayed_project_removal', where: 'delayed_project_removal = TRUE'
+  end
+end

db/schema_migrations/20210923135909

+2afb8292fcdf9a56c11d9404275ffecfde4b2a474e733e3e19f4db62c628aa6c
\ No newline at end of file

db/structure.sql

@@ -16178,8 +16178,7 @@ CREATE TABLE namespaces (
     push_rule_id bigint,
     shared_runners_enabled boolean DEFAULT true NOT NULL,
     allow_descendants_override_disabled_shared_runners boolean DEFAULT false NOT NULL,
-    traversal_ids integer[] DEFAULT '{}'::integer[] NOT NULL,
-    delayed_project_removal boolean DEFAULT false NOT NULL
+    traversal_ids integer[] DEFAULT '{}'::integer[] NOT NULL
 );
 
 CREATE SEQUENCE namespaces_id_seq
@@ -26915,8 +26914,6 @@ CREATE UNIQUE INDEX term_agreements_unique_index ON term_agreements USING btree
 
 CREATE INDEX tmp_idx_deduplicate_vulnerability_occurrences ON vulnerability_occurrences USING btree (project_id, report_type, location_fingerprint, primary_identifier_id, id);
 
-CREATE INDEX tmp_idx_on_namespaces_delayed_project_removal ON namespaces USING btree (id) WHERE (delayed_project_removal = true);
-
 CREATE INDEX tmp_index_namespaces_empty_traversal_ids_with_child_namespaces ON namespaces USING btree (id) WHERE ((parent_id IS NOT NULL) AND (traversal_ids = '{}'::integer[]));
 
 CREATE INDEX tmp_index_namespaces_empty_traversal_ids_with_root_namespaces ON namespaces USING btree (id) WHERE ((parent_id IS NULL) AND (traversal_ids = '{}'::integer[]));