gcp: remove never-successful violation field renames

[efd6]

Proposed commit message

The rename refers to fields that do not exist in the type, and appears to
have been incorrectly added to the block handling PolicyViolationInfo.

The alternative would have been to add the following, but we already
document the current behaviour, so leaving this as is as unfortunate.

  - foreach:
      field: gcp.audit.policy_violation_info.violations
      ignore_missing: true
      ignore_failure: true
      processor:
        rename:
          field: _ingest._value.errorMessage
          target_field: _ingest._value.error_message
      if: ctx.gcp?.audit?.policy_violation_info?.violations instanceof List
  - foreach:
      field: gcp.audit.policy_violation_info.violations
      ignore_missing: true
      ignore_failure: true
      processor:
        rename:
          field: _ingest._value.checkedValue
          target_field: _ingest._value.checked_value
      if: ctx.gcp?.audit?.policy_violation_info?.violations instanceof List
  - foreach:
      field: gcp.audit.policy_violation_info.violations
      ignore_missing: true
      ignore_failure: true
      processor:
        rename:
          field: _ingest._value.policyType
          target_field: _ingest._value.policy_type
      if: ctx.gcp?.audit?.policy_violation_info?.violations instanceof List

[1]https://cloud.google.com/logging/docs/reference/audit/auditlog/rest/Shared.Types/AuditLog#ViolationInfo

Thanks to @ishleenk17 for identifying this.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.
• I have verified that any added dashboard complies with Kibana's Dashboard good practices

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