[ML] Decommission the 7.17 branch build 💔

[edsavage]

The 7.17 build has reached EOL. It no longer requires building.

[prodsecmachine]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scanner	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues
✅	Licenses	0	0	0	0	0 issues

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[valeriy42]

We need to keep it buildable and in sync with Elasticsearch 7.17 for potential urgent fixes even though it's after EOL.