refactor(lib/schemes): remove useless assertions

[Fdawgs]

\b is useless here as it is always at a word boundary because it is preceded by a word character (a-f) or a non-word character (\d number), and followed by a non-word character (hyphen).

Checklist

• run npm run test and npm run benchmark
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct