Revert "Merge branch '54924-clean-up-data' into 'master'"

This reverts commit c9ecc71a, reversing
changes made to c3c8dbf8.

db/migrate/20190228092516_clean_up_noteable_id_for_notes_on_commits.rb

-# frozen_string_literal: true
-
-# See http://doc.gitlab.com/ce/development/migration_style_guide.html
-# for more information on how to write migrations for GitLab.
-
-class CleanUpNoteableIdForNotesOnCommits < ActiveRecord::Migration[5.0]
-  include Gitlab::Database::MigrationHelpers
-
-  # Set this constant to true if this migration requires downtime.
-  DOWNTIME = false
-
-  TEMP_INDEX_NAME = 'index_notes_on_commit_with_null_noteable_id'
-
-  disable_ddl_transaction!
-
-  def up
-    remove_concurrent_index_by_name(:notes, TEMP_INDEX_NAME)
-
-    add_concurrent_index(:notes, :id, where: "noteable_type = 'Commit' AND noteable_id IS NOT NULL", name: TEMP_INDEX_NAME)
-
-    # rubocop:disable Migration/UpdateLargeTable
-    update_column_in_batches(:notes, :noteable_id, nil) do |table, query|
-      query.where(
-        table[:noteable_type].eq('Commit').and(table[:noteable_id].not_eq(nil))
-      )
-    end
-
-    remove_concurrent_index_by_name(:notes, TEMP_INDEX_NAME)
-  end
-
-  def down
-  end
-end

spec/migrations/clean_up_noteable_id_for_notes_on_commits_spec.rb

-# frozen_string_literal: true
-
-require 'spec_helper'
-require Rails.root.join('db', 'migrate', '20190228092516_clean_up_noteable_id_for_notes_on_commits.rb')
-
-describe CleanUpNoteableIdForNotesOnCommits, :migration do
-  let(:notes) { table(:notes) }
-
-  before do
-    notes.create!(noteable_type: 'Commit', commit_id: '3d0a182204cece4857f81c6462720e0ad1af39c9', noteable_id: 3, note: 'Test')
-    notes.create!(noteable_type: 'Commit', commit_id: '3d0a182204cece4857f81c6462720e0ad1af39c9', noteable_id: 3, note: 'Test')
-    notes.create!(noteable_type: 'Commit', commit_id: '3d0a182204cece4857f81c6462720e0ad1af39c9', noteable_id: 3, note: 'Test')
-
-    notes.create!(noteable_type: 'Issue', noteable_id: 1, note: 'Test')
-    notes.create!(noteable_type: 'MergeRequest', noteable_id: 1, note: 'Test')
-    notes.create!(noteable_type: 'Snippet', noteable_id: 1, note: 'Test')
-  end
-
-  it 'clears noteable_id for notes on commits' do
-    expect { migrate! }.to change { dirty_notes_on_commits.count }.from(3).to(0)
-  end
-
-  it 'does not clear noteable_id for other notes' do
-    expect { migrate! }.not_to change { other_notes.count }
-  end
-
-  def dirty_notes_on_commits
-    notes.where(noteable_type: 'Commit').where('noteable_id IS NOT NULL')
-  end
-
-  def other_notes
-    notes.where("noteable_type != 'Commit' AND noteable_id IS NOT NULL")
-  end
-end