Use native rust-bitcoin methods for weight calculations (#360)

See #353

This deletes the custom `weight.rs` traits and `input_type.rs` helpers
in favor of out-of-the-box rust-bitcoin methods. It also removes the
unused `output_type.rs`.

payjoin/src/lib.rs

@@ -35,8 +35,6 @@ pub use v2::OhttpKeys;
 #[cfg(feature = "io")]
 pub mod io;
 
-#[cfg(any(feature = "send", feature = "receive"))]
-pub(crate) mod input_type;
 #[cfg(any(feature = "send", feature = "receive"))]
 pub(crate) mod psbt;
 #[cfg(any(feature = "send", all(feature = "receive", feature = "v2")))]
@@ -45,8 +43,6 @@ mod request;
 pub use request::*;
 
 mod uri;
-#[cfg(any(feature = "send", feature = "receive"))]
-pub(crate) mod weight;
 
 #[cfg(feature = "base64")]
 pub use bitcoin::base64;