Reduce mobile app error to debug

[balloob]

Breaking change

Proposed change

When a sensor is not registered, we return an error to the sender. We don't need to log this too. #71562 (comment)

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
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Checklist

• The code change is tested and works locally.
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[probot-home-assistant]

Hey there @home-assistant/core, mind taking a look at this pull request as it has been labeled with an integration (mobile_app) you are listed as a code owner for? Thanks!
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[TomBrien]

Much better