twl6030 battery: remove ac_next_refresh

We now update capacity estimates using the gas gauge. No need to
schedule voltage-based estimates except when voltage is critically low.
(This reconciliation based on voltages will be done in a later patch).
So remove this code.

Change-Id: I46706c954e32667a84a4e64c9a0831a706755da8
Signed-off-by: Sivakumar Pothireddy <sivakumar.pothireddy@ti.com>
Signed-off-by: Anand Gadiyar <gadiyar@ti.com>