Remove support for script tags.

sdk/lib/_internal/compiler/implementation/dart_backend/utils.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.
 
 part of dart_backend;
 
 class CloningVisitor implements Visitor<Node> {
   final TreeElements originalTreeElements;
   final TreeElementMapping cloneTreeElements;
 
@@ skipping 151 matching lines @@
 
   visitParenthesizedExpression(ParenthesizedExpression node) =>
       new ParenthesizedExpression(visit(node.expression), node.beginToken);
 
   visitRethrow(Rethrow node) => new Rethrow(
       node.throwToken, node.endToken);
 
   visitReturn(Return node) => new Return(
       node.beginToken, node.endToken, visit(node.expression));
 
-  visitScriptTag(ScriptTag node) => new ScriptTag(
-      visit(node.tag), visit(node.argument),
-      visit(node.prefixIdentifier), visit(node.prefix),
-      node.beginToken, node.endToken);
-
   visitSend(Send node) => new Send(
       visit(node.receiver), visit(node.selector), visit(node.argumentsNode));
 
   visitSendSet(SendSet node) => new SendSet(
       visit(node.receiver), visit(node.selector),
       visit(node.assignmentOperator), visit(node.argumentsNode));
 
   visitStringInterpolation(StringInterpolation node) =>
       new StringInterpolation(visit(node.string), visit(node.parts));
 
@@ skipping 99 matching lines @@
   }
 
   Node visitStringNode(StringNode node) {
     unimplemented('visitNode', node: node);
   }
 
   unimplemented(String message, {Node node}) {
     throw message;
   }
 }