power: remove POWER_SUPPLY_PROP_CAPACITY_LEVEL

The CAPACITY_LEVEL stuff defines various levels of charge; however, what
is the difference between them?  What differentiates between HIGH and NORMAL,
LOW and CRITICAL, etc?

As it appears that these are fairly arbitrary, we end up making such policy
decisions in the kernel (or in hardware).  This is the sort of decision that
should be made in userspace, not in the kernel.

If the hardware does not support _CAPACITY and it cannot be easily calculated,
then perhaps the driver should register a custom CAPACITY_LEVEL attribute;
however, userspace should not become accustomed to looking for such a thing,
and we should certainly not encourage drivers to provide CAPACITY_LEVEL
stubs.

The following removes support for POWER_SUPPLY_PROP_CAPACITY_LEVEL.  The
OLPC battery driver is the only driver making use of this, so it's
removed from there as well.

Signed-off-by: Andres Salomon <dilinger@debian.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>