Merge rust-bitcoin#4698: Remove amount serde traits

37eb78b Remove amount serde traits (Tobin C. Harding)

Pull request description:

  Now that a `SignedAmount` can be infallibly converted to an `Amount` we do not need all the internal complexity in the `amount::serde` module, we can just de/serialize `SignedAmount` and convert it to `Amount`. This also has the advantage if someone has a type that is `Into<SignedAmount>` and `TryFrom<SignedAmount>` they can de/serialize it also - BOOM!
  
  Props to Kix for the idea.
  
  Close: rust-bitcoin#4674


ACKs for top commit:
  apoelstra:
    ACK 37eb78b; successfully ran local tests


Tree-SHA512: aadfda15828a9140af73e29ebd72353b0aba85850424eeb293e0ea22060b8fe3b082f39cbbf7af1a37dbf5b17a7575a2d03430269c17f73bee1743430de48206

Author: apoelstra