[RegisterConfiguration] Streamline access to arch defaults, simplify Registers.

test/unittests/compiler/instruction-selector-unittest.cc

Index: test/unittests/compiler/instruction-selector-unittest.cc
diff --git a/test/unittests/compiler/instruction-selector-unittest.cc b/test/unittests/compiler/instruction-selector-unittest.cc
index a0a78916602306b28d9d869157e7fbf21466ce2b..936a94ee6b60ec569a48903c5f8e6c409fdf6f15 100644
--- a/test/unittests/compiler/instruction-selector-unittest.cc
+++ b/test/unittests/compiler/instruction-selector-unittest.cc
@@ -45,9 +45,8 @@ InstructionSelectorTest::Stream InstructionSelectorTest::StreamBuilder::Build(
   selector.SelectInstructions();
   if (FLAG_trace_turbo) {
     OFStream out(stdout);
-    PrintableInstructionSequence printable = {
-        RegisterConfiguration::ArchDefault(RegisterConfiguration::TURBOFAN),
-        &sequence};
+    PrintableInstructionSequence printable = {RegisterConfiguration::Turbofan(),
+                                              &sequence};
     out << "=== Code sequence after instruction selection ===" << std::endl
         << printable;
   }