lxd-agent: Drop aggregated cpu stats in metrics
lxd-agent: Drop aggregated cpu stats in metrics

The aggregated CPU stats should be dropped for two reasons:

1) To be consistent as containers don't have them
2) These stats can be calculated using the other CPU stats

This resolves #9322.

Signed-off-by: Thomas Hipp <5f82c492b3b00e427412d216ce820707a10c51ce@canonical.com>

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