sql/catalog: lease manager won't return prior versions of dropped descriptors

[thoszhang]

From the comments for lease.Manager.Acquire():

// Acquire acquires a read lease for the specified descriptor ID valid for
// the timestamp. It returns the descriptor and a expiration time.
// A transaction using this descriptor must ensure that its
// commit-timestamp < expiration-time. Care must be taken to not modify
// the returned descriptor.
//
// Known limitation: Acquire() can return an error after the descriptor with
// the ID has been dropped. This is true even when using a timestamp
// less than the timestamp of the DROP command. This is because Acquire
// can only return an older version of a descriptor if the latest version
// can be leased; as it stands a dropped descriptor cannot be leased.

Further discussion in #31776 and #18354.

Jira issue: CRDB-3880

[ajwerner]

This was so close to being fixed, but isn't. It would be nice to fix this.

[ajwerner]

See #61493 for reverting an attempt at this. The problem was we lacked the use of export request to find the right portion of the descriptor history. This was fixed in #71239.