Update Modal component with new button component
We need to make sure that all components in GitLab UI use the latest button component.
https://gitlab.com/groups/gitlab-org/-/epics/1049#note_283029837 discusses the strategy to get the button component fully integrated after which we can update the components as well.
---
> Align the production `gl-button` with the design system, which means merge changes of the `gl-new-button` into the `gl-button`. This will allow the `gl-modal` to pass the `visual_gitlab_integration` job.
If this is completed the folowing task originally from https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/issues/282 can be completed
- [ ] Banner on vue tab that warns of incorrect styling is removed from Pajamas
- [x] Remove banner implemented by https://gitlab.com/gitlab-org/gitlab-ui/-/merge_requests/1064
issue