Remove extranous holder load in some prototype-chain checking cases

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index 9a3166ee40ba8a94f7fe9dd3b9c0fca0973c6a36..3b82b470c321f60bf04dbb8db604582cf37d3ddf 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -1843,7 +1843,7 @@ LInstruction* LChunkBuilder::DoCheckInstanceType(HCheckInstanceType* instr) {
 LInstruction* LChunkBuilder::DoCheckPrototypeMaps(HCheckPrototypeMaps* instr) {
   LUnallocated* temp = TempRegister();
   LCheckPrototypeMaps* result = new(zone()) LCheckPrototypeMaps(temp);
-  return AssignEnvironment(Define(result, temp));
+  return AssignEnvironment(result);
 }