chore(nargo)!: remove flat_witness feature flag (#2208)

chore!: remove `flat_witess` feature flag

crates/nargo_cli/Cargo.toml

@@ -61,5 +61,4 @@ default = ["plonk_bn254"]
 # The plonk backend can only use bn254, so we do not specify the field
 plonk_bn254 = ["acvm-backend-barretenberg/native"]
 plonk_bn254_wasm = ["acvm-backend-barretenberg/wasm"]
-flat_witness = ["acvm-backend-barretenberg/native"]
 

crates/nargo_cli/src/backends.rs

@@ -1,6 +1,6 @@
 pub(crate) use acvm_backend_barretenberg::Barretenberg as ConcreteBackend;
 
-#[cfg(not(any(feature = "plonk_bn254", feature = "plonk_bn254_wasm", feature = "flat_witness")))]
+#[cfg(not(any(feature = "plonk_bn254", feature = "plonk_bn254_wasm")))]
 compile_error!("please specify a backend to compile with");
 
 #[cfg(all(feature = "plonk_bn254", feature = "plonk_bn254_wasm"))]

crates/nargo_cli/src/cli/fs/witness.rs

@@ -14,30 +14,9 @@ pub(crate) fn save_witness_to_dir<P: AsRef<Path>>(
     create_named_dir(witness_dir.as_ref(), "witness");
     let witness_path = witness_dir.as_ref().join(witness_name).with_extension(WITNESS_EXT);
 
-    let buf: Vec<u8> = serialize_witness_map(witnesses)?;
+    let buf: Vec<u8> = witnesses.try_into()?;
 
     write_to_file(buf.as_slice(), &witness_path);
 
     Ok(witness_path)
 }
-
-#[cfg(not(feature = "flat_witness"))]
-fn serialize_witness_map(witnesses: WitnessMap) -> Result<Vec<u8>, FilesystemError> {
-    let buf: Vec<u8> = witnesses.try_into()?;
-    Ok(buf)
-}
-
-#[cfg(feature = "flat_witness")]
-fn serialize_witness_map(witnesses: WitnessMap) -> Result<Vec<u8>, FilesystemError> {
-    let mut buf: Vec<u8> = Vec::new();
-    let mut counter = 1;
-    for (index, value) in witnesses {
-        while counter < index.witness_index() {
-            buf.extend(vec![0; 32]);
-            counter += 1;
-        }
-        buf.extend_from_slice(&value.to_be_bytes());
-        counter += 1;
-    }
-    Ok(buf)
-}