Undo unreleased changes from transforming-media.md

The "Transforming media" page has been updated with changes that won't
be part of the next release. Undo these changes so that this page is
consistent with the latest release.

PiperOrigin-RevId: 503917637
(cherry picked from commit fdf86661)

docs/transforming-media.md

@@ -70,8 +70,8 @@ Transformer.Listener transformerListener =
      }
 
      @Override
-     public void onTransformationError(MediaItem inputMediaItem, TransformationException e) {
-       displayError(e);
+     public void onTransformationError(MediaItem inputMediaItem, TransformationException exception) {
+       displayError(exception);
      }
    };
 ~~~