Remove recently introduced FunctionType vm class by merging it into class Type.

runtime/lib/type_patch.dart

Index: runtime/lib/type_patch.dart
diff --git a/runtime/lib/type_patch.dart b/runtime/lib/type_patch.dart
index 5d0f305bc0780a9e3d5d5e9161f406c4661587ae..67d7db5345f4f47ae3babbb2d0f877169cc482eb 100644
--- a/runtime/lib/type_patch.dart
+++ b/runtime/lib/type_patch.dart
@@ -13,10 +13,6 @@ abstract class _AbstractType implements Type {
 class _Type extends _AbstractType {
 }
 
-// Equivalent of RawFunctionType.
-class _FunctionType extends _AbstractType {
-}
-
 // Equivalent of RawTypeRef.
 class _TypeRef extends _AbstractType {
 }