As found by suganthi.mani@mongodb.com, this OpObserver is not filtering on namespaces for deletes at the moment (i.e. it is set to kAll).

The implicit filtering is dependent on:
PrimaryOnlyServiceRegistry::lookupServerByNamespace() only has services registered that have getStateDocumentsNS() that pertain to the config db. Here is the full list of currently overridden methods, all of which are within the config db.

• kShardMergeRecipientsNamespace
• kTenantMigrationDonorsNamespace
• kTenantMigrationRecipientsNamespace
• kConfigsvrCoordinatorsNamespace
• kGlobalIndexClonerNamespace
• kMultiUpdateCoordinatorsNamespace
• kShardingRenameParticipantsNamespace
• kConfigReshardingOperationsNamespace
• kDonorReshardingOperationsNamespace
• kRecipientReshardingOperationsNamespace
• kShardingDDLCoordinatorsNamespace
• kShardSplitDonorsNamespace
• kSetChangeStreamStateCoordinatorNamespace