ARM: dts: omap3-igep: Remove NAND partition table

FDT harcoded partition table does not match that one in historical
TI's 2.6.37 kernel and non legacy kernels even use different ECC scheme,
yet noone complained, so remove it altogether.
Also, UBI volumes instead of partitions are used since u-boot-2016.09.

Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>