Implement best practices for Bitcoin Providers

[matthewjablack]

Description

This PR improves BitcoinCollateralProvider and BitcoinCollateralSwapProvider to follow best practices.

Submission Checklist :pencil:

• [x] QSP BP 25. Remove TODO's
• [x] QSP BP 31. Remove duplicated code
• [x] QSP BP 32. Remove unused variables/constants
• [x] QSP BP 33. Fix ambiguous error messages in constructor