Remove unnecessary de-duplication.

Follow up on https://crrev.com/c/1113036/2/my_activity.py#752

R=sergiyb@chromium.org

Change-Id: I56e4936f2f2bc94a734aeb510594ee8384d6e2a9
Reviewed-on: https://chromium-review.googlesource.com/1121816Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>

my_activity.py

@@ -749,7 +749,7 @@ class MyActivity(object):
     changes_without_issue = []
     for change in self.changes:
       added = False
-      for issue_uid in set(change['bugs']):
+      for issue_uid in change['bugs']:
         if issue_uid in issues:
           changes_by_issue_uid[issue_uid].append(change)
           added = True