fix: Remove unused overlay visibility tracking in MatchingPairsGame c…

…lass as the information was already being stored and this was causing an error

backend/experiment/rules/matching_pairs.py

@@ -140,7 +140,6 @@ def calculate_intermediate_score(self, session, result):
         second_card = result_data["second_card"]
         second_section = Section.objects.get(pk=second_card["id"])
         second_card["filename"] = str(second_section.filename)
-        overlay_was_shown = result_data["overlay_was_shown"]
         if first_section.group == second_section.group:
             if "seen" in second_card and second_card["seen"]:
                 score = 20