Fix bulk delete button inside trash documentation

According to the documentation here:
https://doc.nuxeo.com/userdoc/1010/content-delete/#trash-search

See this picture:
https://doc.nuxeo.com/assets/userdoc/1010/content-delete/trash-search-selected-web-ui.png

There should be an icon for bulk permanently deleting documents.

It is actually missing. (see missing_button.png)
This can be reproduced in 10.10 and nightly.nuxeo.com.