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

src/mips/lithium-mips.cc

Index: src/mips/lithium-mips.cc
diff --git a/src/mips/lithium-mips.cc b/src/mips/lithium-mips.cc
index c64533cdfcbd10201c743179160bbb1efc888667..49f4222c5dca62e763d9b5d1d93db603d7e1965f 100644
--- a/src/mips/lithium-mips.cc
+++ b/src/mips/lithium-mips.cc
@@ -1652,13 +1652,6 @@ LInstruction* LChunkBuilder::DoCompareObjectEqAndBranch(
 }
 
 
-LInstruction* LChunkBuilder::DoCompareConstantEqAndBranch(
-    HCompareConstantEqAndBranch* instr) {
-  return new(zone()) LCmpConstantEqAndBranch(
-      UseRegisterAtStart(instr->value()));
-}
-
-
 LInstruction* LChunkBuilder::DoIsObjectAndBranch(HIsObjectAndBranch* instr) {
   ASSERT(instr->value()->representation().IsTagged());
   LOperand* temp = TempRegister();