Remove spec fill_in_checkout_form repeat define

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/127440



Merged-by: Allen Cook <acook@gitlab.com>
Approved-by: Ross Byrne <robyrne@gitlab.com>
Approved-by: Allen Cook <acook@gitlab.com>
Co-authored-by: Linjie Zhang <ljzhang@gitlab.cn>