… underlying migration task" test (#233995) (#234540)

# Backport

This will backport the following commits from `main` to `8.19`:
- [[Security Solution][Detection Engine] removes FTR "deletes the
underlying migration task" test
(#233995)](#233995)

<!--- Backport version: 10.0.2 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sorenlouv/backport)

<!--BACKPORT [{"author":{"name":"Vitalii
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Solution][Detection Engine] removes FTR \"deletes the underlying
migration task\" test (#233995)\n\n## Summary\n\n- addresses
https://github.com/elastic/kibana/issues/179593\n- removes FTR \"deletes
the underlying migration task\" test\n- test was skipped from the moment
it was introduced, 5 yers ago
-\nhttps://github.com//pull/85690/files#diff-d3ab7ab5d42b0e7dfe7a3162188693eb420f0a819444aa36380148f2a450a6dbR166-R185,\nso
was never functional\n- While looked at code of [finalize
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[Security Solution][Detection Engine] removes FTR \"deletes the
underlying migration task\" test (#233995) (#234430)\n\n#
Backport\n\nThis will backport the following commits from `main` to
`9.1`:\n- [[Security Solution][Detection Engine] removes FTR \"deletes
the\nunderlying migration task\"
test\n(#233995)](https://github.com/elastic/kibana/pull/233995)\n\n\n\n###
Questions ?\nPlease refer to the [Backport
tool\ndocumentation](https://github.com/sorenlouv/backport)\n\n\n\nCo-authored-by:
Vitalii Dmyterko
<92328789+vitaliidm@users.noreply.github.com>"}},{"branch":"8.19","label":"v8.19.0","branchLabelMappingKey":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"url":"https://github.com/elastic/kibana/pull/234429","number":234429,"state":"OPEN"},{"branch":"main","label":"v9.2.0","branchLabelMappingKey":"^v9.2.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/233995","number":233995,"mergeCommit":{"message":"[Security
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-\nhttps://github.com//pull/85690/files#diff-d3ab7ab5d42b0e7dfe7a3162188693eb420f0a819444aa36380148f2a450a6dbR166-R185,\nso
was never functional\n- While looked at code of [finalize
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did not see any indications, it actually deletes underlying
migration\ntask\n- since this API is deprecated anyway, the most
reasonable approach\nseems just to remove that
test","sha":"980469abd01528b8c3ad6959fe35f240d95e3584"}}]}] BACKPORT-->