Remove deprecated speed conversion functions

[davet2001]

Breaking change

Should not be a breaking change. Custom integrations have been warned of deprecation since 2022.10.

Proposed change

The pressure conversion functions have been replaced, and the deprecation period has passed.
Please use homeassistant.util.unit_conversion.SpeedConverter.convert() instead.

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 #
• This PR is related to issue: Deprecate conversion utilities #78957
• Link to documentation pull request: Create blog post for clean up of deprecated unit conversion functions developers.home-assistant#1942

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
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• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

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