Use config entry setup in cast tests

[emontnemery]

Proposed change

Use config entry setup in cast tests

Support for configuring cast through YAML was removed in December 2021, but code was kept around because it was needed for tests.

This PR adjust the tests to use YAML and removes the code related to YAML setup.

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)
• Deprecation (breaking change to happen in the future)
• 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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[gjohansson-ST]

Also needs remove import step in config flow

[home-assistant]

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