batteryservice: Remove remnants of CAF's HVDCP changes

Commit 86e9bc79 removed the usage
of isHvdcpPresent(), but did not remove the function itself.

Remove isHvdcpPresent() as clean-up.

This essentially reverts the rest of the following commits:
9f8e6008 batteryservice: Avoid exception if device doesn't support HVDCP
4df4f532 batteryservice: add support for charger led blinking

Change-Id: Ie39c11ee9811f6af84a55ed85b72123cc449c735