r8169: remove some WOL-related dead code

Commit bde135a6 "r8169: only enable PCI wakeups when WOL is active"
removed the only user of flag RTL_FEATURE_WOL. So let's remove some
now dead code.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>