Remove `BootstrapModalConfirm` and use `ConfirmDialog` instead

## Description

It looks like the [BootstrapModalConfirm](https://github.com/Graylog2/graylog2-server/blob/931aa91fa2e5bf3150dc7b6540bcc1d16aaadb80/graylog2-web-interface/src/components/bootstrap/BootstrapModalConfirm.tsx) and [ConfirmDialog](https://github.com/Graylog2/graylog2-server/blob/931aa91fa2e5bf3150dc7b6540bcc1d16aaadb80/graylog2-web-interface/src/components/common/ConfirmDialog.tsx) serve the same purpose, and we could replace one with the other.

For example, this bug could likely have been avoided if we had used `ConfirmDialog` instead of `BootstrapModalConfirm`, because the `ConfirmDialog` uses a different z-index. https://github.com/Graylog2/graylog2-server/issues/23253.