Avoid using FunctionSignature in builder_kernel

pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:js_runtime/shared/embedded_names.dart';
 import 'package:kernel/ast.dart' as ir;
 
 import '../closure.dart';
 import '../common.dart';
 import '../compiler.dart';
@@ skipping 201 matching lines @@
   @override
   Local getLocal(ir.VariableDeclaration variable) {
     // If this is a synthetic local, return the synthetic local
     if (variable.name == null) {
       return _syntheticLocals.putIfAbsent(
           variable, () => new SyntheticLocal("x", null, null));
     }
     return getElement(variable) as LocalElement;
   }
 
-  FunctionSignature getFunctionSignature(ir.FunctionNode function) {
-    return getElement(function).asFunctionElement().functionSignature;
-  }
-
   // Is the member a lazy initialized static or top-level member?
   bool isLazyStatic(ir.Member member) {
     if (member is ir.Field) {
       FieldElement field = _nodeToElement[member];
       return field.constant == null;
     }
     return false;
   }
 
   KernelJumpTarget getJumpTarget(ir.TreeNode node,
@@ skipping 396 matching lines @@
   TypeMask selectorTypeOf(Selector selector, TypeMask mask) {
     return TypeMaskFactory.inferredTypeForSelector(
         selector, mask, _globalInferenceResults);
   }
 
   TypeMask typeFromNativeBehavior(
       native.NativeBehavior nativeBehavior, ClosedWorld closedWorld) {
     return TypeMaskFactory.fromNativeBehavior(nativeBehavior, closedWorld);
   }
 }