Fix sort on Audit page provider

Steps to reproduce

1. navigate to an existing document
2. make a modification
3. navigate to the History tab
4. clic on the column Date to make a ASC sort
5. observe the data are correctly sorted, from the oldest to the newest
6. clic again on the column Date to make a DESC sort
7. observe that the same result is returned => problem

Expected behavior: when a DESC sort is requested, the data should be sorted from the newest to the oldest

The problem seems to come from the getSortInfos method which always initialized the sort infos with 2 sorts : https://github.com/nuxeo/nuxeo/blob/master/modules/platform/nuxeo-elasticsearch/nuxeo-elasticsearch-audit/src/main/java/org/nuxeo/elasticsearch/audit/pageprovider/ESDocumentHistoryPageProvider.java#L104 => why?