Revert "Build Observatory with runtime"

runtime/bin/vmservice/observatory/lib/src/app/view_model.dart

 // Copyright (c) 2014, 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 app;
 
 abstract class TableTreeRow extends Observable {
   final TableTreeRow parent;
   @observable final int depth;
   @observable final List<TableTreeRow> children = new List<TableTreeRow>();
@@ skipping 193 matching lines @@
     if (column != _sortColumnIndex) {
       return columns[column].label + '\u2003';
     }
     return columns[column].label + (_sortDescending ? arrowUp : arrowDown);
   }
 
   dynamic getValue(int row, int column) {
     return rows[row].values[column];
   }
 }