Update observatory_tool.py to remove package-root

runtime/observatory/observatory.gypi

 # 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.
 
 {
   'variables': {
     'gen_source_dir': '<(SHARED_INTERMEDIATE_DIR)',
   },
   'targets': [
     {
@@ skipping 11 matching lines @@
             '<(SHARED_INTERMEDIATE_DIR)/packages.stamp',
             'pubspec.yaml',
           ],
           'outputs': [
             '<(gen_source_dir)/observatory_packages.stamp'
           ],
           'action': [
             'python',
             '../tools/observatory_tool.py',
             '--sdk=True',
-            '--package-root', '<(PRODUCT_DIR)/packages',
             '--stamp',
             '<(gen_source_dir)/observatory_packages.stamp',
             '--dart-executable',
             '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)dart_bootstrap<(EXECUTABLE_SUFFIX)',
             '--directory', 'observatory',
             '--command', 'get',
           ],
         }
       ],
     },
@@ skipping 16 matching lines @@
             '<(gen_source_dir)/observatory_packages.stamp',
             '<@(_sources)',
           ],
           'outputs': [
             '<(PRODUCT_DIR)/observatory/build/web/index.html',
           ],
           'action': [
             'python',
             '../tools/observatory_tool.py',
             '--sdk=True',
-            '--package-root', '<(PRODUCT_DIR)/packages',
             '--dart-executable',
             '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)dart_bootstrap<(EXECUTABLE_SUFFIX)',
             '--directory', 'observatory',
             '--command', 'build',
             '<(PRODUCT_DIR)/observatory/build'
           ],
         },
         {
           'action_name': 'deploy_observatory',
           'inputs': [
             '../../tools/observatory_tool.py',
             '<(PRODUCT_DIR)/observatory/build/web/index.html',
           ],
           'outputs': [
             '<(PRODUCT_DIR)/observatory/deployed/web/index.html',
           ],
           'action': [
             'python',
             '../tools/observatory_tool.py',
             '--sdk=True',
-            '--package-root', '<(PRODUCT_DIR)/packages',
             '--dart-executable',
             '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)dart_bootstrap<(EXECUTABLE_SUFFIX)',
             '--directory', '<(PRODUCT_DIR)/observatory/',
             '--command', 'deploy',
           ],
         }
       ],
     },
   ],
 }