Genuine ES behaviour for getTotalHits()

In response to the issue https://github.com/FriendsOfSymfony/FOSElasticaBundle/issues/746

This minor edit allows `RawPaginatorAdapter::getTotalHits()` to return the real total count (i.e. all matching documents).

By default, the total is limited to the size query parameter, which doesn't comply with elasticsearch api.

It is useful when you only need to count the number of documents that correspond to a given query, without actually retrieving any document.