Drop present_at_unpublish column from attachment data table

Now that we are no longer marking attachments as present at unpublishing as part of unpublishing a document, this database column is no longer needed.

db/migrate/20231020151031_drop_present_at_unpublishing_column_from_attachments.rb

@@ -0,0 +1,5 @@
+class DropPresentAtUnpublishingColumnFromAttachments < ActiveRecord::Migration[7.0]
+  def change
+    remove_column :attachment_data, :present_at_unpublish, :boolean
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.0].define(version: 2023_10_16_170633) do
+ActiveRecord::Schema[7.0].define(version: 2023_10_20_151031) do
   create_table "assets", charset: "utf8mb3", force: :cascade do |t|
     t.string "asset_manager_id", null: false
     t.string "variant", null: false
@@ -30,7 +30,6 @@
     t.datetime "created_at", precision: nil
     t.datetime "updated_at", precision: nil
     t.integer "replaced_by_id"
-    t.boolean "present_at_unpublish"
     t.index ["replaced_by_id"], name: "index_attachment_data_on_replaced_by_id"
   end