Repl rename support adds unnecessary duplication for non-rename alters

Currently, the rename events contain a before & after object. For non-rename cases, we simply impress the "after" object, and thus have no need of the "before" object. Thus, we might want to minimize wastage by not materializing "before" if this is a non-rename case.

Also worth considering - if a rename case, do we really need the before object, or simply the before & after names?

Having before & after objects is good in that it allows us flexibility, but we might not need that much info. From a perf viewpoint, we might want to trim things a bit here.