Remove startup_url from PageSet, we can now only specify startup_url on a Page.

tools/telemetry/telemetry/page/page_set.py

Index: tools/telemetry/telemetry/page/page_set.py
diff --git a/tools/telemetry/telemetry/page/page_set.py b/tools/telemetry/telemetry/page/page_set.py
index 682f06966293a437533f822a2732eca920a3b888..3246ff64dc26036c78f13271489fc4ba59f520c0 100644
--- a/tools/telemetry/telemetry/page/page_set.py
+++ b/tools/telemetry/telemetry/page/page_set.py
@@ -22,8 +22,8 @@ class PageSetError(Exception):
 
 class PageSet(user_story_set.UserStorySet):
   def __init__(self, file_path=None, archive_data_file='', user_agent_type=None,
-               make_javascript_deterministic=True, startup_url='',
-               serving_dirs=None, bucket=None):
+               make_javascript_deterministic=True, serving_dirs=None,
+               bucket=None):
     super(PageSet, self).__init__()
     # The default value of file_path is location of the file that define this
     # page set instance's class.
@@ -39,8 +39,6 @@ class PageSet(user_story_set.UserStorySet):
     self.user_agent_type = user_agent_type
     self.make_javascript_deterministic = make_javascript_deterministic
     self._wpr_archive_info = None
-    self.startup_url = startup_url
-    self.user_stories = []
     # Convert any relative serving_dirs to absolute paths.
     self._serving_dirs = set(os.path.realpath(os.path.join(self.base_dir, d))
                              for d in serving_dirs or [])