Revert of Reland: Remove register index/code indirection

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 211e4ba927cf8108fd9328c451277a07e9616d6b..5093624dbd63e018854d737a7e24c4071c833e1e 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -13526,10 +13526,10 @@
       int assigned_reg = op->index();
       if (op->IsDoubleRegister()) {
         trace_.Add(" \"%s\"",
-                   DoubleRegister::from_code(assigned_reg).ToString());
+                   DoubleRegister::AllocationIndexToString(assigned_reg));
       } else {
         DCHECK(op->IsRegister());
-        trace_.Add(" \"%s\"", Register::from_code(assigned_reg).ToString());
+        trace_.Add(" \"%s\"", Register::AllocationIndexToString(assigned_reg));
       }
     } else if (range->IsSpilled()) {
       LOperand* op = range->TopLevel()->GetSpillOperand();