fix (experiment): #2165 use default top sites feed for screenshots experiment
fix (experiment): #2165 use default top sites feed for screenshots experiment

JaredKerim-Mozilla/activity-stream,mozilla/activity-stream,rlr/activity-streams,rlr/activity-streams,mozilla/activity-stream,AdamHillier/activity-stream,mozilla/activity-streams,sarracini/activity-stream,mozilla/activity-streams,rlr/activity-streams,Mardak/activity-stream,rlr/activity-streams,JaredKerim-Mozilla/activity-stream,Mardak/activity-stream,sarracini/activity-stream,sarracini/activity-stream,JaredKerim-Mozilla/activity-stream,AdamHillier/activity-stream,sarracini/activity-stream,Mardak/activity-stream,mozilla/activity-stream,JaredKerim-Mozilla/activity-stream,AdamHillier/activity-stream,AdamHillier/activity-stream,mozilla/activity-stream,Mardak/activity-stream