FIX: Let user clear their flair group (PR #13669)

Users were able to select their flair, but were not able to clear it by selecting (none).

GitHub

      fab!(:group) { Fabricate(:group, name: "Group", flair_bg_color: "#111111", flair_color: "#999999", flair_icon: "icon") }
      fab!(:user) { Fabricate(:user) }