Remove unused cleanup script

src/Plugin/migrate/process/CleanHtml.php

-<?php
-
-namespace Drupal\cambridge_migrations\Plugin\migrate\process;
-
-use Drupal\migrate\ProcessPluginBase;
-use Drupal\migrate\MigrateExecutableInterface;
-use Drupal\migrate\Row;
-
-/**
- * Clean up HTML content by removing unwanted JSON media entries.
- *
- * @MigrateProcessPlugin(
- *   id = "clean_html"
- * )
- */
-class CleanHtml extends ProcessPluginBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
-    if (empty($value)) {
-      return $value;
-    }
-
-    // Remove JSON media entries wrapped in <p> tags
-    $value = preg_replace('/<p>\[\[{.*?"type":"media".*?}\]\]<\/p>/s', '', $value);
-
-    // Remove any standalone JSON media entries
-    $value = preg_replace('/\[\[{.*?"type":"media".*?}\]\]/s', '', $value);
-
-    // Clean up multiple blank lines that might be left after removing content
-    $value = preg_replace('/(\r?\n){2,}/', "\n\n", $value);
-    $value = preg_replace('/<p>\s*<\/p>/', '', $value);
-
-    return trim($value);
-  }
-}