Revert of Convert SIMD wasm ops to runtime function calls

src/compiler/simd-lowering.h

-// Copyright 2016 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_SIMD_LOWERING_H_
-#define V8_COMPILER_SIMD_LOWERING_H_
-
-#include "src/compiler/graph-reducer.h"
-#include "src/compiler/wasm-compiler.h"
-#include "src/runtime/runtime.h"
-
-namespace v8 {
-namespace internal {
-namespace compiler {
-
-typedef Signature<Conversion> ConversionSignature;
-
-class SimdLowering final : public Reducer {
- public:
-  SimdLowering(Zone* zone, WasmGraphBuilder* builder)
-      : builder_(builder), zone_(zone) {
-    InitializeSignatures();
-  }
-  virtual ~SimdLowering();
-  Reduction Reduce(Node* node) override;
-
- private:
-  WasmGraphBuilder* builder_;
-  Zone* zone_;
-
-  void InitializeSignatures();
-};
-
-}  // namespace compiler
-}  // namespace internal
-}  // namespace v8
-
-#endif  // V8_COMPILER_SIMD_LOWERING_H_