net: sh-eth: remove sh_eth_offset_rz table

First, this table could never be included in the build anyway because
SH_ETH_TYPE_RZ is not defined until later in the file.
Second, the register PIR was missing, so PHY MDIO never worked.
Third, after adding the PIR register, the table is EXACTLY the same as
sh_eth_offset_gigabit, so there is no value to it.

Therefore, just delete it use the gigabit one.

Signed-off-by: Chris Brandt <chris.brandt@renesas.com>
Acked-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>