🌱 Remove deprecated ClusterResourceSet feature gate

[aman4433]

What this PR does / why we need it:
This PR removes the deprecated ClusterResourceSet feature gate, which has been GA since v1.11.

Ref: Remove previously deprecated code

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Task of #12771
Fixes #11114

[aman4433]

/test pull-cluster-api-test-main

[aman4433]

/test pull-cluster-api-e2e-blocking-main

[k8s-ci-robot]

@aman4433: 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	46de674	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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[sbueringer]

/test pull-cluster-api-e2e-main-gke

[sbueringer]

Thank you very much!!

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 9988271cb6f12ac6bdc71227ba132fa07588c367

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sbueringer

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