linaro-base.conf: remove CONFIG_NFS_V2 is not set

Upstream defconfigs set CONFIG_NFS_V2=y, which is needed to test kernel
with NFSroot. However when we merge the linaro-base.conf, it disables
CONFIG_NFS_V2, which caused NFS mount failure.

Since NFS_V2 is enabled by default in the upstream defconfigs, removing
line "CONFIG_NFS_V2 is not set" will keep it enabled and fix the
problem.

Signed-off-by: Chase Qi <chase.qi@linaro.org>
Acked-by: Kevin Hilman <khilman@linaro.org>