When we try to create an ident that already exists and is in the drop-pending state, we ignore the drop timestamp and immediately drop the ident. This should be safe as the only way for this to happen is if we rolled back the creation of the ident and thus there cannot be any readers, but it has the potential to magnify the impact of other bugs. We should refine this to only ignore the drop timestamp of idents dropped as part of startup recovery, as this is the only time that a never-fully-committed ident should have a drop timestamp.