[deoptimizer] Remove obsolete DeoptInfo::mnemonic field.

src/deoptimizer.cc

Index: src/deoptimizer.cc
diff --git a/src/deoptimizer.cc b/src/deoptimizer.cc
index 3e699922de9f1ed0b4d802b7b9bebe3777b3ae88..d6794a5c53c4a33da5bb2608ccf04c08e5a8c70c 100644
--- a/src/deoptimizer.cc
+++ b/src/deoptimizer.cc
@@ -2651,7 +2651,7 @@ Deoptimizer::DeoptInfo Deoptimizer::GetDeoptInfo(Code* code, Address pc) {
              RelocInfo::ModeMask(RelocInfo::POSITION);
   for (RelocIterator it(code, mask); !it.done(); it.next()) {
     RelocInfo* info = it.rinfo();
-    if (info->pc() >= pc) return DeoptInfo(last_position, NULL, last_reason);
+    if (info->pc() >= pc) return DeoptInfo(last_position, last_reason);
     if (info->rmode() == RelocInfo::POSITION) {
       int raw_position = static_cast<int>(info->data());
       last_position = raw_position ? SourcePosition::FromRaw(raw_position)
@@ -2660,7 +2660,7 @@ Deoptimizer::DeoptInfo Deoptimizer::GetDeoptInfo(Code* code, Address pc) {
       last_reason = static_cast<Deoptimizer::DeoptReason>(info->data());
     }
   }
-  return DeoptInfo(SourcePosition::Unknown(), NULL, Deoptimizer::kNoReason);
+  return DeoptInfo(SourcePosition::Unknown(), Deoptimizer::kNoReason);
 }