This makes the deletion mapreduce more resilient in the face of data integrity
violations (which exist on sandbox but hopefully not in production). Even when
the domain application index doesn't exist, we still want to delete the domain
application itself, as its continuing presence will cause problems after the
code for domain applications is deleted.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=228521794