[turbofan] Remove unused PlainPrimitiveToNumber operator.

src/compiler/js-typed-lowering.cc

Index: src/compiler/js-typed-lowering.cc
diff --git a/src/compiler/js-typed-lowering.cc b/src/compiler/js-typed-lowering.cc
index bde4af1f03ad4672aa0fe1f3e6335cecb3f7f5b5..0f8d76afc16729c4fb362e7c9e2e8dc2b1dc27f5 100644
--- a/src/compiler/js-typed-lowering.cc
+++ b/src/compiler/js-typed-lowering.cc
@@ -247,7 +247,6 @@ class JSBinopReduction final {
     // Avoid inserting too many eager ToNumber() operations.
     Reduction const reduction = lowering_->ReduceJSToNumberInput(node);
     if (reduction.Changed()) return reduction.replacement();
-    // TODO(jarin) Use PlainPrimitiveToNumber once we have it.
     return graph()->NewNode(
         javascript()->ToNumber(), node, jsgraph()->NoContextConstant(),
         jsgraph()->EmptyFrameState(), graph()->start(), graph()->start());