Update to a more recent version of rust-bitcoin

[luckysori]

When tackling #1912, I would have liked to be able to use certain functionality that is not present in version 0.29.2.

I gave it a go, but the upgrade path is not so simple because rust-dlc still depends on 0.29.2 (although Tibo was thinking about upgrading in the near future) and our version of rust-lightning still depends on 0.29.2 too.

Blocked by:

• Removing unused rust-lightning dependencies.
• Updating rust-dlc, if any rust-bitcoin types are used across crate boundaries.