Change removing of fields, to work with tests.

Closes #3383366

src/Plugin/search_api/processor/Synonyms.php

@@ -125,6 +125,18 @@ class Synonyms extends FieldsProcessorPluginBase implements PluginFormInterface
     }
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function defaultConfiguration() {
+    $configuration = parent::defaultConfiguration();
+
+    unset($configuration['all_fields']);
+    unset($configuration['fields']);
+
+    return $configuration;
+  }
+
   /**
    * {@inheritdoc}
    */
@@ -147,12 +159,8 @@ class Synonyms extends FieldsProcessorPluginBase implements PluginFormInterface
    * {@inheritdoc}
    */
   public function buildConfigurationForm(array $form, FormStateInterface $form_state): array {
-    $form = parent::buildConfigurationForm($form, $form_state);
     $config = $this->configFactory->get('search_api_meilisearch.settings');
-    // Remove fields select form element because the Meilisearch doesn't
-    // provide a way to set synonyms per field.
-    unset($form['all_fields']);
-    unset($form['fields']);
+
     $synonyms = $config->get('meilisearch_synonyms')[$this->getIndex()->id()] ?? '';
     $form['synonyms'] = [
       '#type' => 'textarea',