[x64] Fix useless deopt in for-in.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1157423003

Cr-Commit-Position: refs/heads/master@{#28692}

src/x64/lithium-codegen-x64.cc

@@ -5884,8 +5884,6 @@ void LCodeGen::DoOsrEntry(LOsrEntry* instr) {
 void LCodeGen::DoForInPrepareMap(LForInPrepareMap* instr) {
   DCHECK(ToRegister(instr->context()).is(rsi));
 
-  DeoptimizeIf(equal, instr, Deoptimizer::kNull);
-
   Condition cc = masm()->CheckSmi(rax);
   DeoptimizeIf(cc, instr, Deoptimizer::kSmi);