idpf: remove legacy Page Pool Ethtool stats

Page Pool Ethtool stats are deprecated since the Netlink Page Pool
interface introduction.
idpf receives big changes in Rx buffer management, including &page_pool
layout, so keeping these deprecated stats does only harm, not speaking
of that CONFIG_IDPF selects CONFIG_PAGE_POOL_STATS unconditionally,
while the latter is often turned off for better performance.
Remove all the references to PP stats from the Ethtool code. The stats
are still available in their full via the generic Netlink interface.

Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>