docs(config-conventional): remove spurious body-leading-blank and footer-leading-blank values

[scop]

Description

These don't take a value.

Motivation and Context

Usage examples

// commitlint.config.js
module.exports = {};

echo "your commit message here" | commitlint # fails/passes

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[escapedcat]

Not sure why the checks don't complete. If this isn't green tomorrow I'll merge it anyways. Sometimes this happens and I'm not really sure what's causing this.