Fix 56 hints in pkg/compiler

pkg/compiler/lib/src/tree_ir/optimization/variable_merger.dart

 // Copyright (c) 2015, 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.
 
 library tree_ir.optimization.variable_merger;
 
 import 'optimization.dart' show Pass;
 import '../tree_ir_nodes.dart';
-import '../../elements/elements.dart' show Local, ParameterElement;
 
 /// Merges variables based on liveness and source variable information.
 ///
 /// This phase cleans up artifacts introduced by the translation through CPS,
 /// where each source variable is translated into several copies. The copies
 /// are merged again when they are not live simultaneously.
 class VariableMerger extends RecursiveVisitor implements Pass {
   String get passName => 'Variable merger';
 
   void rewrite(RootNode node) {
@@ skipping 521 matching lines @@
     // VariableDeclaration is only used for captured variables, which are never
     // merged, so this is not strictly necessary. But it's nicer if this class
     // works for arbitrary substitution maps.
     node.variable = replaceWrite(node.variable);
     node.value = visitExpression(node.value);
     node.next = visitStatement(node.next);
     return node;
   }
 
 }