Fix SABnzbd config check

[shaiu]

Proposed change

1. keep old sensor keys for config check
2. remove CONF_URL from CONFIG_SCHEMA (new) so check won't fail because it's not present in old configuration yaml

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 is related to issue: SABnzbd sensors not linked to the integration #71303

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the [development checklist][dev-checklist]
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

The integration reached or maintains the following [Integration Quality Scale][quality-scale]:

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