Revert "BatteryService: privatize battery light observer"

Both pointless and missing a SEMICOLON.

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This reverts commit 8ab8ca7c8307efd6b0817ae6e367d29585c4df67.

Change-Id: I897a5ca5cb5ec87633ea517e83075d090ba7cfec
Merge "Revert "BatteryService: privatize battery light observer"" into kk44