[AKS] remove unsupported properties from managed cluster agent pool

[mboersma]

These fields were mistakenly copied from ContainerServiceAgentPoolProfile and was never supported by AKS. storageProfile is supported but only accepts "ManagedDisks" (the default if empty), so making it read-only is a compromise between retaining a property that is in the data model and preventing user confusion.

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Automation for azure-sdk-for-python

The initial PR has been merged into your service PR:
Azure/azure-sdk-for-python#2954

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The initial PR has been merged into your service PR:
Azure/azure-sdk-for-go#2342

[weinong]

@mboersma the agentpool profile is defined at https://github.com/Azure/acs-engine/blob/master/pkg/api/agentPoolOnlyApi/v20170831/types.go#L139
It doesn't have dnsPrefix, fqdn, and storageProfile

[weinong]

Also, regex on ContainerServiceNetworkProfile.podCidr may need to allow empty string.
@JunSun17 to confirm

[JunSun17]

I do not think we should allow empty string for podCidr. It should be ok as it is for now.

[zqingqing1]

@sarangan12 Can you help to review this PR?