ARC: nSIM_700: remove unused network options

We have snps,arc-emac enabled in nSIM_700. It's obsolete and it's
not used anymore so remove its device tree node and disable
unused network options in defconfig.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>