tg3: Remove dead code

Now that CPMU devices don't do MAC loopback, all the CPMU power saving
mode adjustments are unneeded.  This patch removes the dead code.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>