[turbofan] Tester improvements; use CSignature and simplify ReturnValueTraits.

test/cctest/compiler/test-simplified-lowering.cc

Index: test/cctest/compiler/test-simplified-lowering.cc
diff --git a/test/cctest/compiler/test-simplified-lowering.cc b/test/cctest/compiler/test-simplified-lowering.cc
index d1bc803cbb7c3596f3e59ef70566778ddb1ff9be..9b2346934c7111e147dce2e5142193d4322ef908 100644
--- a/test/cctest/compiler/test-simplified-lowering.cc
+++ b/test/cctest/compiler/test-simplified-lowering.cc
@@ -33,11 +33,8 @@ template <typename ReturnType>
 class SimplifiedLoweringTester : public GraphBuilderTester<ReturnType> {
  public:
   SimplifiedLoweringTester(MachineType p0 = kMachNone,
-                           MachineType p1 = kMachNone,
-                           MachineType p2 = kMachNone,
-                           MachineType p3 = kMachNone,
-                           MachineType p4 = kMachNone)
-      : GraphBuilderTester<ReturnType>(p0, p1, p2, p3, p4),
+                           MachineType p1 = kMachNone)
+      : GraphBuilderTester<ReturnType>(p0, p1),
         typer(this->isolate(), this->graph(), MaybeHandle<Context>()),
         javascript(this->zone()),
         jsgraph(this->isolate(), this->graph(), this->common(), &javascript,