fix deletion for azureManagedControlPlane while using existing RG

[LochanRn]

What type of PR is this?
/kind bug

What this PR does / why we need it:
Fixes deletion of AMCP while using existing RG

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 #1441

Special notes for your reviewer: None

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

NONE

[k8s-ci-robot]

Hi @LochanRn. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[alexeldeib]

/ok-to-test

this aligns managed RG deletion to the same behavior as AzureCluster, as context (we discussed it offline).

[LochanRn]

/test pull-cluster-api-provider-azure-e2e-windows

[alexeldeib]

/lgtm

[CecileRobertMichon]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: CecileRobertMichon

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