pm2301: Remove volt_now & curr_now properties

There is no support to measure the main charger voltage and
current using AB9540 gpadc. Therefore this has been removed
from the driver.

Signed-off-by: Rajkumar Kasirajan <rajkumar.kasirajan@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Michel JAOUEN <michel.jaouen@stericsson.com>
Reviewed-by: Rabin VINCENT <rabin.vincent@stericsson.com>
Tested-by: Michel JAOUEN <michel.jaouen@stericsson.com>