Reorganize hir_ty modules

Chalk isn't really a 'traits' thing anymore, so it doesn't make sense to
have all the Chalk-related stuff in submodules of `traits`.

crates/hir_ty/src/infer/expr.rs

@@ -20,7 +20,8 @@ use crate::{
     method_resolution, op,
     primitive::{self, UintTy},
     static_lifetime, to_chalk_trait_id,
-    traits::{chalk::from_chalk, FnTrait},
+    traits::FnTrait,
+    chalk_db::from_chalk,
     utils::{generics, Generics},
     AdtId, Binders, CallableDefId, FnPointer, FnSig, FnSubst, InEnvironment, Interner,
     ProjectionTyExt, Rawness, Scalar, Substitution, TraitRef, Ty, TyBuilder, TyExt, TyKind,