ARM: tegra: nexus7: Remove monitored-battery property

The bq27541 Linux kernel driver will try to reprogram controller based
on the values from monitored-battery node, but it fails to do so because
controller was locked by manufacturer. Still this is a very undesirable
behaviour, hence let's remove the optional battery node.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>