feat(BroadcastMessage): Remove alert role

mentioned in commit e00707c2

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!133 (merged)

mentioned in merge request status-page!757 (merged)

mentioned in merge request gitlab!117429 (merged)

mentioned in merge request gitlab!117558 (closed)

mentioned in merge request gitlab-docs!3774 (merged)

mentioned in merge request gitlab-docs!3775 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3352 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3353 (merged)

mentioned in merge request gitlab!118205 (merged)

mentioned in merge request gitlab!118387 (closed)