Remove swap_column_names migration helper

as per code review.

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/64577.

db/post_migrate/20210622041846_finalize_push_event_payloads_bigint_conversion.rb

@@ -32,7 +32,11 @@ class FinalizePushEventPayloadsBigintConversion < ActiveRecord::Migration[6.1]
     add_concurrent_foreign_key TABLE_NAME, :events, column: :event_id_convert_to_bigint, on_delete: :cascade
 
     with_lock_retries(raise_on_exhaustion: true) do
-      swap_column_names TABLE_NAME, :event_id, :event_id_convert_to_bigint # rubocop:disable Migration/WithLockRetriesDisallowedMethod
+      # Swap column names
+      temp_name = 'event_id_tmp'
+      execute "ALTER TABLE #{quote_table_name(TABLE_NAME)} RENAME COLUMN #{quote_column_name(:event_id)} TO #{quote_column_name(temp_name)}"
+      execute "ALTER TABLE #{quote_table_name(TABLE_NAME)} RENAME COLUMN #{quote_column_name(:event_id_convert_to_bigint)} TO #{quote_column_name(:event_id)}"
+      execute "ALTER TABLE #{quote_table_name(TABLE_NAME)} RENAME COLUMN #{quote_column_name(temp_name)} TO #{quote_column_name(:event_id_convert_to_bigint)}"
 
       # Swap defaults
       change_column_default TABLE_NAME, :event_id, nil

lib/gitlab/database/migration_helpers.rb

@@ -1616,17 +1616,6 @@ into similar problems in the future (e.g. when new tables are created).
         raise
       end
 
-      def swap_column_names(table_name, column_1, column_2)
-        unless transaction_open?
-          raise 'Cannot call swap_column_names without a transaction open or outside of a transaction block.'
-        end
-
-        temp_name = "#{column_1}_tmp"
-        execute "ALTER TABLE #{quote_table_name(table_name)} RENAME COLUMN #{quote_column_name(column_1)} TO #{quote_column_name(temp_name)}"
-        execute "ALTER TABLE #{quote_table_name(table_name)} RENAME COLUMN #{quote_column_name(column_2)} TO #{quote_column_name(column_1)}"
-        execute "ALTER TABLE #{quote_table_name(table_name)} RENAME COLUMN #{quote_column_name(temp_name)} TO #{quote_column_name(column_2)}"
-      end
-
       def rename_constraint(table_name, old_name, new_name)
         execute <<~SQL
           ALTER TABLE #{quote_table_name(table_name)}

spec/lib/gitlab/database/migration_helpers_spec.rb

@@ -2978,53 +2978,6 @@ RSpec.describe Gitlab::Database::MigrationHelpers do
     end
   end
 
-  describe '#swap_column_names' do
-    let(:table) { :_test_table }
-    let(:ar_model) do
-      Class.new(ActiveRecord::Base) do
-        self.table_name = :_test_table
-      end
-    end
-
-    before do
-      model.drop_table table, if_exists: true
-      model.create_table table, id: false do |t|
-        t.integer :column_1
-        t.bigint  :column_2
-      end
-
-      model.add_index(table, :column_2)
-    end
-
-    after do
-      model.drop_table table, if_exists: true
-    end
-
-    it 'swaps column names as requested' do
-      model.swap_column_names(table, :column_1, :column_2)
-
-      column_1 = ar_model.column_for_attribute(:column_1)
-      column_2 = ar_model.column_for_attribute(:column_2)
-
-      expect(column_1.sql_type).to eq('bigint')
-      expect(column_2.sql_type).to eq('integer')
-    end
-
-    it 'does not rename indexes' do
-      model.swap_column_names(table, :column_1, :column_2)
-
-      index = model.indexes_for(table, :column_1).first
-      expect(index.name).to eq("index_#{table}_on_column_2")
-    end
-
-    it 'raises an error when not in transaction' do
-      expect(model).to receive(:transaction_open?).and_return(false)
-
-      expect { model.swap_column_names(table, :column_1, :column_2) }
-        .to raise_error 'Cannot call swap_column_names without a transaction open or outside of a transaction block.'
-    end
-  end
-
   describe '#rename_constraint' do
     it "executes the statement to rename constraint" do
       expect(model).to receive(:execute).with /ALTER TABLE "test_table"\nRENAME CONSTRAINT "fk_old_name" TO "fk_new_name"/