Remove now-unnecessary blueprint generics.

These were needed before as a way to _partially deserialize_
  blueprints. Indeed, some commands required accessing information of
  the blueprint, but not necessarily the schema. So out of laziness (or
  cleverness?), we only deserialized validators as serde::Value and
  achieved that through the use of generics.

  Now that validators and schemas have proper deserialisers, we can
  simply deserialize a blueprint.

  TODO: Our serialisation/deserialisation is safe with regards to
  itself; i.e. it roundtrips. However, we only supports a subset of the
  specified blueprint format. For example, we would fail to deserialize
  blueprints that have inline data-schemas (we only use references).

crates/aiken/src/cmd/blueprint/convert.rs

@@ -65,7 +65,7 @@ pub fn exec(
         .map_err(|_| BlueprintError::InvalidOrMissingFile)
         .into_diagnostic()?;
 
-    let blueprint: Blueprint<serde_json::Value, serde_json::Value> =
+    let blueprint: Blueprint =
         serde_json::from_reader(BufReader::new(blueprint)).into_diagnostic()?;
 
     // Perform the conversion