Pluaralize ComputePolicies operation group

[begoldsm]

This was missed during initial swagger review. This new group should by
pluralized since it also contains an object called "ComputePolicy"

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[begoldsm]

@amarzavery I do not believe this has resulted in anything being published yet, so this should not be a breaking change. I have not triggered any publish jobs and the AutoRestCI PRs triggered from the original change (#1182) are both still open, so we should be good to merge this and then publish from these changes.