Remove celery check to improve search page performance

[chiatt]

Checking for the availability of a celery worker is an expensive call that can take between 1 and 6 seconds. We call this on every load of the search page to confirm that celery is available for large search exports. If it's not available and a user is trying to export more instances than is allowed without celery, we notify the user that they must reduce their search because celery isn't running. This isn't very helpful to most users who aren't going to know what vegetables have to do with their search export.

We should just remove this check entirely and simply inform users that their search exceeds the export limit and that they have to refine it.