Add example how to remove config entry from device

[mib1185]

Proposed change

This adds an example how to remove a config entry from a device registry entry.

Type of change

• [ ] Document existing features within Home Assistant
• [ ] Document new or changing features which there is an existing pull request elsewhere
• [x] Spelling or grammatical corrections, or rewording for improved clarity
• [ ] Changes to the backend of this documentation
• [ ] Removed stale or deprecated documentation

Additional information

• This PR fixes or closes issue: fixes #
• Link to relevant existing code or pull request:

[home-assistant[bot]]

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