AO3-6676 Remove participant memoization causing Leave button to appear on all collection blurbs #3775

Job	Run time
rake db:otwseed	1m 31s
rspec spec/controllers	9m 52s
rspec spec/models	5m 12s
rspec --exclude-pattern 'spec/{controllers,models}/*/.rb'	5m 1s
cucumber features/admins	5m 12s
cucumber features/bookmarks	4m 27s
cucumber features/collections	5m 36s
cucumber features/comments_and_kudos	5m 55s
cucumber features/gift_exchanges	6m 19s
cucumber features/importing	2m 37s
cucumber features/other_a	9m 41s
cucumber features/other_b	6m 9s
cucumber features/prompt_memes_a	4m 11s
cucumber features/prompt_memes_b	3m 31s
cucumber features/prompt_memes_c	4m 37s
cucumber features/search	6m 11s
cucumber features/tag_sets	3m 13s
cucumber features/tags_and_wrangling	5m 58s
cucumber features/users	4m 54s
cucumber features/works	13m 56s
	1h 54m 3s

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