usage.adoc: remove lonely closing parenthesis

[ghost]

Type of change

Description: Fixes minor typo

Select the type of change(s) made in this pull request:

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [x] Documentation (change or fix to documentation)

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Fixes no issue

Proposed changes

[Rafiot]

Thank you!