DEV: Drop old hotlinked image data from post_custom_fields (#16594)

`20220428094026_create_post_hotlinked_media` moved this data into a dedicated table

db/post_migrate/20220429164301_delete_hotlinked_image_custom_fields.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+class DeleteHotlinkedImageCustomFields < ActiveRecord::Migration[7.0]
+  disable_ddl_transaction!
+
+  def up
+    execute <<~SQL
+      DELETE FROM post_custom_fields
+      WHERE name IN (
+        'downloaded_images',
+        'broken_images',
+        'large_images'
+      )
+    SQL
+
+    execute <<~SQL
+      DROP INDEX CONCURRENTLY IF EXISTS post_custom_field_broken_images_idx
+    SQL
+
+    execute <<~SQL
+      DROP INDEX CONCURRENTLY IF EXISTS post_custom_field_downloaded_images_idx
+    SQL
+
+    execute <<~SQL
+      DROP INDEX CONCURRENTLY IF EXISTS post_custom_field_large_images_idx
+    SQL
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end