init: hack for /charger symlink

Legacy symlink from /charger to /system/bin/charger is
removed. Instead, all Android R devices are required
to use /system/bin/charger instead.

See hardware/interfaces/health/2.1/README.md for details.

Bug: 142286265
Test: charger mode
Change-Id: Ib478a864ef68647bc9fc14650ca3d382952b80c8