⚠️ Remove deprecated flag for old infra machine naming

[mboersma]

What this PR does / why we need it:

Removes the flag --use-deprecated-infra-machine-naming, which was planned to disappear in CAPI v1.9.

Which issue(s) this PR fixes:
Refs #10576
Refs #11172

/area provider/control-plane-kubeadm
/area machineset

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[mboersma]

/cc @lentzi90

[k8s-ci-robot]

@mboersma: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cluster-api-apidiff-main	35b6b0c	link	false	/test pull-cluster-api-apidiff-main

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[lentzi90]

Could we get #11172 merged first?

[adilGhaffarDev]

Could we get #11172 merged first?

/hold
The above PR is required prior to removing this flag.

[sbueringer]

Could we get #11172 merged first?

Yup, absolutely. I should get around to 11172 soon