Update observatory_tool.py to remove package-root

tools/bots/bot.py

Index: tools/bots/bot.py
diff --git a/tools/bots/bot.py b/tools/bots/bot.py
index b24fe74139bd1bc9aaa559ab9e3fc7ffe251d5cf..92a4f97643025193a7537c662fccb91663bd070b 100644
--- a/tools/bots/bot.py
+++ b/tools/bots/bot.py
@@ -255,7 +255,6 @@ def RunTestRunner(build_info, path):
 
   build_root = utils.GetBuildRoot(
       BUILD_OS, build_info.mode, build_info.arch)
-  package_root = os.path.abspath(os.path.join(build_root, 'packages'))
 
   dart_name = 'dart.exe' if build_info.system == 'windows' else 'dart'
   dart_bin = os.path.join(sdk_bin, dart_name)
@@ -264,9 +263,7 @@ def RunTestRunner(build_info, path):
       os.path.join('third_party', 'pkg', 'test', 'bin', 'test.dart'))
 
   with utils.ChangedWorkingDirectory(path):
-    args = [dart_bin, '--package-root=' + package_root, test_bin,
-            '--package-root', package_root, '--reporter', 'expanded',
-            '--no-color']
+    args = [dart_bin, test_bin, '--reporter', 'expanded', '--no-color']
     print("Running %s" % ' '.join(args))
     RunProcess(args)