fix: remove unused `title-sr-only` prop in `modal.js`

mentioned in commit 63e77a59

mentioned in merge request gitlab-org/frontend/playground/accessibility-scanner!58 (merged)

mentioned in merge request status-page!903

mentioned in merge request gitlab!174711 (merged)

mentioned in merge request gitlab!174879 (merged)

mentioned in merge request gitlab!174890 (closed)

mentioned in merge request gitlab-org/editor-extensions/gitlab-jetbrains-plugin!1361 (closed)

mentioned in merge request gitlab!174941 (closed)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!4209 (closed)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!4210 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!4211 (closed)

mentioned in merge request gitlab-org/editor-extensions/gitlab-jetbrains-plugin!1407 (closed)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!358 (closed)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!359 (merged)

mentioned in merge request gitlab-org/editor-extensions/gitlab-jetbrains-plugin!1446 (closed)