ethtool: fec: remove long structure description

Digging through the mailing list archive @autoneg was part
of the first version of the RFC, this left over comment was
pointed out twice in review but wasn't removed.

The sentence is an exact copy-paste from pauseparam.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>