Remove HCompareConstantEqAndBranch (never used), and its corresponding Lithium instructions.

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 5bd5dc70fabb9063b612c674ff9e2bff64430d07..b6ce1281f174354c5972a8b330dda492017033aa 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -1652,13 +1652,6 @@ LInstruction* LChunkBuilder::DoCompareObjectEqAndBranch(
 }
 
 
-LInstruction* LChunkBuilder::DoCompareConstantEqAndBranch(
-    HCompareConstantEqAndBranch* instr) {
-  LOperand* value = UseRegisterAtStart(instr->value());
-  return new(zone()) LCmpConstantEqAndBranch(value);
-}
-
-
 LInstruction* LChunkBuilder::DoIsObjectAndBranch(HIsObjectAndBranch* instr) {
   ASSERT(instr->value()->representation().IsTagged());
   return new(zone()) LIsObjectAndBranch(UseRegisterAtStart(instr->value()));