[turbofan] Remove the TryLowerDirectJSCall hack from generic lowering.

src/compiler/js-generic-lowering.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_JS_GENERIC_LOWERING_H_
 #define V8_COMPILER_JS_GENERIC_LOWERING_H_
 
 #include "src/code-factory.h"
 #include "src/compiler/graph-reducer.h"
 #include "src/compiler/linkage.h"
@@ skipping 23 matching lines @@
   // Dispatched depending on opcode.
   JS_OP_LIST(DECLARE_LOWER)
 #undef DECLARE_LOWER
 
   // Helpers to replace existing nodes with a generic call.
   void ReplaceWithCompareIC(Node* node, Token::Value token);
   void ReplaceWithStubCall(Node* node, Callable c, CallDescriptor::Flags flags);
   void ReplaceWithBuiltinCall(Node* node, Builtins::JavaScript id, int args);
   void ReplaceWithRuntimeCall(Node* node, Runtime::FunctionId f, int args = -1);
 
-  // Helper for optimization of JSCallFunction.
-  bool TryLowerDirectJSCall(Node* node);
-
   Zone* zone() const;
   Isolate* isolate() const;
   JSGraph* jsgraph() const { return jsgraph_; }
   Graph* graph() const;
   CommonOperatorBuilder* common() const;
   MachineOperatorBuilder* machine() const;
 
  private:
   bool const is_typing_enabled_;
   JSGraph* const jsgraph_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_JS_GENERIC_LOWERING_H_