Remove the narrow-phase graph indices from the collider.

They are on the narrow-phase now.

src/data/mod.rs

@@ -1,8 +1,10 @@
 //! Data structures modified with guaranteed deterministic behavior after deserialization.
 
+pub use self::coarena::Coarena;
 pub use self::maybe_serializable_data::MaybeSerializableData;
 
 pub mod arena;
+mod coarena;
 pub(crate) mod graph;
 pub(crate) mod hashmap;
 mod maybe_serializable_data;