Reconsider Custom diff handling for Manager Cluster SKU

[mikhailshilkov]

https://github.com/pulumi/pulumi-azure-native/pull/2688 landed a tactic fix for #2600 by adding a custom diff handler around that specific resource.

To minimize maintenance burden over time, we should consider removing this change after more generic mechanisms are in place, tracked in https://github.com/pulumi/pulumi-azure-native/issues/2467 and https://github.com/pulumi/pulumi-azure-native/issues/2552

[cleverguy25]

Added to epic https://github.com/pulumi/home/issues/3552