power: charger-manager: Get external power souce information only from EXTCON.

power: charger-manager: Get external power souce information only from EXTCON.

When charger-manager checks whether external power source is available,
it gets information from charger IC driver. However, it's not correct source,
charger IC doesn't have responsibilty to give cable connection status.
The charger-manager already gets cable information from EXTCON susbsystem,
so it can re-use it.

Change-Id: I408546beefe63707fcb927db7d92c4005f3848f8
Signed-off-by: Jonghwa Lee <jonghwa3.lee@samsung.com>