[turbofan] Address a couple of Type-related TODOs.

src/compiler/type-cache.h

Index: src/compiler/type-cache.h
diff --git a/src/compiler/type-cache.h b/src/compiler/type-cache.h
index 4814959eb202b285e99451493fa48ce7edd8f72b..69eaf11616c7d64f8115f5e8f875ae137f979819 100644
--- a/src/compiler/type-cache.h
+++ b/src/compiler/type-cache.h
@@ -35,9 +35,8 @@ class TypeCache final {
   Type* const kFloat32 = Type::Number();
   Type* const kFloat64 = Type::Number();
 
-  Type* const kSmi = Type::SignedSmall();
-  Type* const kHoleySmi = Type::Union(kSmi, Type::Hole(), zone());
-  Type* const kHeapNumber = Type::Number();
+  Type* const kHoleySmi =
+      Type::Union(Type::SignedSmall(), Type::Hole(), zone());
 
   Type* const kSingletonZero = CreateRange(0.0, 0.0);
   Type* const kSingletonOne = CreateRange(1.0, 1.0);