[arm] Drop SMMLS support.

src/base/bits.cc

 // 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.
 
 #include "src/base/bits.h"
 #include "src/base/logging.h"
 
 namespace v8 {
 namespace base {
 namespace bits {
@@ skipping 14 matching lines @@
   int64_t const value = static_cast<int64_t>(lhs) * static_cast<int64_t>(rhs);
   return bit_cast<int32_t, uint32_t>(bit_cast<uint64_t>(value) >> 32u);
 }
 
 
 int32_t SignedMulHighAndAdd32(int32_t lhs, int32_t rhs, int32_t acc) {
   return bit_cast<int32_t>(bit_cast<uint32_t>(acc) +
                            bit_cast<uint32_t>(SignedMulHigh32(lhs, rhs)));
 }
 
-
-int32_t SignedMulHighAndSub32(int32_t lhs, int32_t rhs, int32_t acc) {
-  return bit_cast<int32_t>(bit_cast<uint32_t>(acc) -
-                           bit_cast<uint32_t>(SignedMulHigh32(lhs, rhs)));
-}
-
-
 }  // namespace bits
 }  // namespace base
 }  // namespace v8