ab8500_charger: Remove unused defines

Cleanup of the ab8500_charger driver.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Marcus Cooper <marcus.xm.cooper@stericsson.com>
Reviewed-by: Karl KOMIEROWSKI <karl.komierowski@stericsson.com>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>