Cleanup nand_info[] declaration.

The nand_info array is declared as extern in several .c files.
Those days, nand.h contains a reference to the array, so there is
no need to declare it elsewhere.

Signed-off-by: Stelian Pop <stelian@popies.net>
Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>