Remove boundary encoding (#2769)

# Description
Now that domain based settlement encoding is stable we can remove the
boundary encoding and configuration variable

# Changes
- [x] Remove boundary encoding logic
- [x] Remove config param

This will also require a infrastructure PR to remove the domain encoding
config variable

## How to test
CI

crates/driver/src/boundary/mod.rs

@@ -23,7 +23,6 @@
 //! Software (2014)
 
 pub mod liquidity;
-pub mod settlement;
 
 // The [`anyhow::Error`] type is re-exported because the legacy code mostly
 // returns that error. This will change as the legacy code gets refactored away.
@@ -32,7 +31,6 @@ pub use {
     anyhow::{Error, Result},
     contracts,
     model::order::OrderData,
-    settlement::Settlement,
     shared::ethrpc::Web3,
 };