[turbofan] Remove access to FunctionType from call interface.

src/interface-descriptors.h

Index: src/interface-descriptors.h
diff --git a/src/interface-descriptors.h b/src/interface-descriptors.h
index 4d18c7d1d08963a0ea4acee158fcb43d163fe4f3..650c83a2ad05a9fa72ad94d98e878b7367b352c6 100644
--- a/src/interface-descriptors.h
+++ b/src/interface-descriptors.h
@@ -133,8 +133,6 @@ class CallInterfaceDescriptorData {
     return platform_specific_descriptor_;
   }
 
-  FunctionType* function_type() const { return function_type_; }
-
  private:
   int register_param_count_;
 
@@ -179,7 +177,7 @@ class CallInterfaceDescriptor {
   }
 
   int GetStackParameterCount() const {
-    return data()->function_type()->Arity() - data()->register_param_count();
+    return data()->param_count() - data()->register_param_count();
   }
 
   Register GetRegisterParameter(int index) const {
@@ -196,8 +194,6 @@ class CallInterfaceDescriptor {
     return data()->platform_specific_descriptor();
   }
 
-  FunctionType* GetFunctionType() const { return data()->function_type(); }
-
   static const Register ContextRegister();
 
   const char* DebugName(Isolate* isolate) const;