r8169: remove rtl_wol_shutdown_quirk()

Since f658b909 ("r8169: fix DMA being used after buffer free if WoL is
enabled") it has been redundant to disable PCI bus mastering in
rtl_wol_shutdown_quirk(). And since 12006848

 ("r8169: fix failing WoL")
CmdRxEnb is still enabled when we get here. So we can remove the function.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/2391ada0-eac5-ac43-f061-a7a44b0e7f33@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>