dspace_statistics_api/indexer.py: Update comment

I don't remember why we needed the stats, but it seems that it was
because without them there is no way to know how many results were
returned and therefore no way to know how many pages we'll need to
iterate over. Having the total number allows us to use a limit and
and offset to page through them deterministically.

dspace_statistics_api/indexer.py

@@ -40,7 +40,8 @@ def index_views():
     # get total number of distinct facets for items with a minimum of 1 view,
     # otherwise Solr returns all kinds of weird ids that are actually not in
     # the database. Also, stats are expensive, but we need stats.calcdistinct
-    # so we can get the countDistinct summary.
+    # so we can get the countDistinct summary to calculate how many pages of
+    # results we have.
     #
     # see: https://lucene.apache.org/solr/guide/6_6/the-stats-component.html
     solr_query_params = {