restore: do not fail on missing descriptors during restore cleanup

[kev-cao]

Currently, if a function descriptor is missing during restore cleanup, restore fails and the job is put in a retry loop as it attempts to revert. If restore is performing a cleanup of all descriptors, having a missing descriptor should not fail cleanup.

Jira issue: CRDB-55741

[blathers-crl]

Hi @kev-cao, please add a branch-* label to identify the earliest affected branch for this C-bug

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[blathers-crl]

cc @cockroachdb/disaster-recovery