Remove BlockExpression from the Kernel language.

lib/binary/ast_from_binary.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.
 library kernel.ast_from_binary;
 
 import '../ast.dart';
 import 'tag.dart';
 import 'loader.dart';
 import 'dart:convert';
 import 'package:kernel/transformations/flags.dart';
@@ skipping 642 matching lines @@
         return new AwaitExpression(readExpression());
       case Tag.FunctionExpression:
         return new FunctionExpression(readFunctionNode());
       case Tag.Let:
         var variable = readVariableDeclaration();
         int stackHeight = variableStack.length;
         pushVariableDeclaration(variable);
         var body = readExpression();
         variableStack.length = stackHeight;
         return new Let(variable, body);
-      case Tag.BlockExpression:
-        var body = readBlock();
-        var expression = readExpression();
-        return new BlockExpression(body, expression);
       default:
         throw fail('Invalid expression tag: $tag');
     }
   }
 
   List<MapEntry> readMapEntryList() {
     return new List<MapEntry>.generate(readUInt(), (i) => readMapEntry());
   }
 
   MapEntry readMapEntry() {
@@ skipping 257 matching lines @@
         isFinal: flags & 0x1 != 0,
         isConst: flags & 0x2 != 0);
   }
 
   int readOffset() {
     // Offset is saved as unsigned,
     // but actually ranges from -1 and up (thus the -1)
     return readUInt() - 1;
   }
 }