Cherry pick PR #9259: Revert "Disable BatteryMonitor for Cobalt builds"

[cobalt-github-releaser-bot]

Refer to the original PR: #9259

Reverts #8912

[github-actions]

🤖 Gemini Suggested Commit Message

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cobalt: Re-enable BatteryMonitor

This change reverts the explicit disabling of BatteryMonitor for Cobalt
builds. BatteryMonitor is now allowed to be initialized, restoring
previous functionality for platforms where it is applicable.

Bug: 9259

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[gemini-code-assist]

Code Review

This pull request removes the IS_COBALT build flag check within the BindBatteryMonitor method in services/device/device_service.cc, which previously caused an early return. I have no feedback to provide.