GenericTemplateGlobalProvider::getDataList() shouldn't sort by default

The common use of this method is to fetch a single aggregate value
for use in partial caches within templates. Sorting aggregates in this
scenario will break MSSQL and PostgreSQL and `DataQuery::initialiseQuery()`
will add `$default_sort` as the sort automatically, which never happened before
the merge of e53280c6500e82a28b5ffec1ec3c24d2df9aad87.

The proposed fix is to just not sort any of the aggregates at all in this context.