Update Coordinator: Only schedule a refresh if listenerrs

[balloob]

Breaking change

Proposed change

Data Update Coordinator would always schedule a refresh after a refresh, even if there are no listeners. This could cause a memory leak if the coordinator was no longer used.

Issue found by @bieniu and @amelchio

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

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# Example configuration.yaml

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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[cgtobi]

LGTM