[ti_misp] Add missing event.original cleanup step for threat_attributes data stream.

[marc-gr]

What does this PR do?

Adds missing event.original cleanup in threat_attributes data stream

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.

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[elasticmachine]

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Build stats

• Start Time: 2023-05-17T08:41:22.756+0000

• Duration: 14 min 11 sec

Test stats 🧪

Test	Results
Failed	0
Passed	15
Skipped	0
Total	15

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (2/2)	💚
Files	100.0% (2/2)	💚
Classes	100.0% (2/2)	💚
Methods	100.0% (30/30)	💚 5.814
Lines	86.344% (607/703)	👎 -13.656
Conditionals	100.0% (0/0)	💚

[chemamartinez]

LGTM

[elasticmachine]

Package ti_misp - 1.14.1 containing this change is available at https://epr.elastic.co/search?package=ti_misp

[elasticmachine]

Package ti_misp - 1.14.1 containing this change is available at https://epr.elastic.co/search?package=ti_misp