net: dsa: delete unused exported symbols for ethtool PHY stats

Introduced in commit cf963573 ("net: dsa: Allow providing PHY
statistics from CPU port"), it appears these were never used.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20220216193726.2926320-1-vladimir.oltean@nxp.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>