net: ena: remove old adaptive interrupt moderation code from ena_netdev

1. Out of the fields {per_napi_bytes, per_napi_packets} in struct ena_ring,
   only rx_ring->per_napi_packets are used to determine if napi did work
   for dim.
   This commit removes all other uses of these fields.
2. Remove ena_ring->moder_tbl_idx, which is not used by dim.
3. Remove all calls to ena_com_destroy_interrupt_moderation(), since all it
   did was to destroy the interrupt moderation table, which is removed as
   part of removing old interrupt moderation code.

Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>