net: ethernet: remove duplicated CONFIG_SUNGEM_PHY entry

Both drivers/net/Kconfig and drivers/net/ethernet/Kconfig contain the
same config entry:

  config SUNGEM_PHY
          tristate

Commit f860b052 ("drivers/net: Kconfig and Makefile cleanup") moved
SUNGEM_PHY from drivers/net/Kconfig to drivers/net/ethernet/Kconfig.

Shortly after it was applied, commit 19e2f6fe ("net: Fix sungem_phy
sharing.") added the second one to drivers/net/Kconfig.

I kept the one in drivers/net/Kconfig because this CONFIG option controls
the compilation of drivers/net/sungem_phy.c.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>