Revert of [stubs] Port SubStringStub to TurboFan

src/code-stubs.cc

Index: src/code-stubs.cc
diff --git a/src/code-stubs.cc b/src/code-stubs.cc
index 4dbd881adfde49da613975e7a75e39e3e0a38d10..e74d408ca62905c41c13d672ab5b22eb53fdf193 100644
--- a/src/code-stubs.cc
+++ b/src/code-stubs.cc
@@ -2686,15 +2686,6 @@
   assembler->UpdateFeedback(var_type_feedback.value(), type_feedback_vector,
                             slot_id);
   return result_var.value();
-}
-
-// ES6 section 21.1.3.19 String.prototype.substring ( start, end )
-compiler::Node* SubStringStub::Generate(CodeStubAssembler* assembler,
-                                        compiler::Node* string,
-                                        compiler::Node* from,
-                                        compiler::Node* to,
-                                        compiler::Node* context) {
-  return assembler->SubString(context, string, from, to);
 }
 
 // ES6 section 7.1.13 ToObject (argument)