power: remove unused poll counter

power: remove unused poll counter

Following the previous fix, there is nothing using the ppi counter.

We can remove the related ppi_av array in struct priority_worker.
This allows us to also remove num_dequeue_pkts_prev and pc from
struct priority_worker since they are only used in conjunction
with the ppi_av array.

Suggested-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>