Remove some warnings and dead code in dart2js.

lib/compiler/implementation/ssa/nodes.dart

 // Copyright (c) 2012, 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.
 
 abstract class HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBailoutTarget(HBailoutTarget node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
   R visitBitOr(HBitOr node);
@@ skipping 571 matching lines @@
 
   void addSuccessor(HBasicBlock block) {
     if (successors.isEmpty()) {
       successors = [block];
     } else {
       successors.add(block);
     }
     block.predecessors.add(this);
   }
 
-  void removeSuccessor(HBasicBlock successor) {
-    successors.removeAt(successors.indexOf(successor));
-    successor.predecessors.removeAt(successors.predecessors.indexOf(this));
-  }
-
   void postProcessLoopHeader() {
     assert(isLoopHeader());
     // Only the first entry into the loop is from outside the
     // loop. All other entries must be back edges.
     for (int i = 1, length = predecessors.length; i < length; i++) {
       loopInformation.addBackEdge(predecessors[i]);
     }
   }
 
   /**
@@ skipping 2372 matching lines @@
   HBasicBlock get start => expression.start;
   HBasicBlock get end {
     // We don't create a switch block if there are no cases.
     assert(!statements.isEmpty());
     return statements.last().end;
   }
 
   bool accept(HStatementInformationVisitor visitor) =>
       visitor.visitSwitchInfo(this);
 }