Do not join corpus table on ListElements + with_corpus=false

The serializer does not give any data about the corpus, but the main query still join on corpus: it's useless and slow downs perfs.

added 1 deleted label

added Optimisation label

mentioned in issue #701 (closed)

The corpus can be deduced either from the URL (for ListElements) or the element (for parents/children), so we should never join on it.

mentioned in merge request !1304 (merged)

mentioned in issue #671 (closed)

closed

mentioned in commit 244b7ac3