Removes the links from the recent actions list in the admin panel.

When allowing extensions to have their own admin sites, broken links are generated by this list under special circumstances. This is due to a bug in Django; an issue has been filed at https://code.djangoproject.com/ticket/17726.

Until a custom admin log is written, or a better solution is found, the links will be removed altogether.

Tested in local dev, observing both the Review Board admin site, and an extension's admin site.