Remove failIfNotExists flag from delete process instance batch operations if unnecessary

[joaquinfelici]

Description

Following-up on the kick-off analysis for Idempotency of change variables batch operation, one question arose regarding the removal of the ifExists flag for the async operations for the deletion of process instances (both runtime and historic): why do we persist the failIfNotExists flag state in the database for Batch Operations but if it cannot be configured? It's used in botch DeleteProcessInstancesJobHandler and DeleteHistoricProcessInstancesJobHandler.

Acceptance Criteria (Required on creation)

• Determine whether the persistence of this flag is required.
• If it's required, explain why.
• If it's not, remove it and adapt the logic.

Hints

• We should have something similar to what we have for set variables batch operation (see pull request).

Links

• https://github.com/camunda/product-hub/issues/2512#issuecomment-2473906341

Breakdown

### Pull Requests

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