⚠️ Remove deprecated Bootstrap Data

[CecileRobertMichon]

What this PR does / why we need it: Machine.Spec.Bootstrap.Data and KubeadmConfigStatus.BootstrapData were deprecated in v1alpha3 in favor of Bootstrap.DataSecretName. This PR removes the deprecated types and all references to them in the codebase and docs.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

[fabriziopandini]

/milestone v0.4.0

[fabriziopandini]

@CecileRobertMichon thanks for this PR!
/lgtm

[ncdc]

@CecileRobertMichon do you need to run make diagrams from the docs dir to regenerate from the plantuml file you changed?

[k8s-ci-robot]

@CecileRobertMichon: The following test failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
pull-cluster-api-apidiff-main	ed9029b	link	/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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[ncdc]

/lgtm

[fabriziopandini]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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