icnss: Remove vbatt feature

Vbatt feature is no longer used and the PMIC ADC
interface is different. Hence remove this feature.

CRs-Fixed: 2095512
Change-Id: Ie46c2b53a37ce812143e41cf19416454b7b26e31
Signed-off-by: Yuanyuan Liu <yuanliu@codeaurora.org>