dart2js cps: Remove dart2dart from cps pipeline and clean up.

pkg/compiler/lib/src/js_backend/codegen/codegen.dart

Index: pkg/compiler/lib/src/js_backend/codegen/codegen.dart
diff --git a/pkg/compiler/lib/src/js_backend/codegen/codegen.dart b/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
index 6379605fcfafc158db3b7d58e526114ac8585bb8..ed8c803cbf88fab50cb10e712280b665d928326c 100644
--- a/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
+++ b/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
@@ -683,29 +683,9 @@ class CodeGenerator extends tree_ir.StatementVisitor
     return glue.generateTypeRepresentation(node.dartType, arguments);
   }
 
-  // Dart-specific IR nodes
-
-  @override
-  visitReifyTypeVar(tree_ir.ReifyTypeVar node) {
-    return errorUnsupportedNode(node);
-  }
-
-  @override
   visitFunctionExpression(tree_ir.FunctionExpression node) {
-    return errorUnsupportedNode(node);
-  }
-
-  @override
-  visitFunctionDeclaration(tree_ir.FunctionDeclaration node) {
-    return errorUnsupportedNode(node);
-  }
-
-  @override
-  visitVariableDeclaration(tree_ir.VariableDeclaration node) {
-    return errorUnsupportedNode(node);
-  }
-
-  errorUnsupportedNode(tree_ir.DartSpecificNode node) {
-    throw "Unsupported node in JS backend: $node";
+    // FunctionExpressions are currently unused.
+    // We might need them if we want to emit raw JS nested functions.
+    throw 'FunctionExpressions should not be used';
   }
 }