Remove all orderings for last collection join with composite keys

[roji]

In #19828, we removed the last ordering for collection joins. We could go further and remove the set of orderings which correspond to the keys of the last collection join, if that join includes composite keys; that would allow us to remove multiple unnecessary orderings, not just one.

See discussion in #24360 (comment) and a draft attempt by @Emill in #24401.

[stevendarby]

@roji do you have any sense of whether removing only the last column in a composite key scenario (i.e. only removing part of the last composite key) will give a perf boost, or is that likely to only come when this issue is fixed and the full key is removed? Just curious!

[roji]

@stevendarby removing the last column (#19828) should still give a perf boost in the composite key scenario - removing an ordering should generally means less work for the database, regardless of whether that ordering is on a part of a composite key or not.