net: Remove remaining remnants of pm_qos from netdevice.h

Commit e2c65448 removed pm_qos from struct net_device but left the
comment and header file. Remove those.

Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>