Remove `design_management_allow_dangerous_images`
<!-- Title suggestion: [Feature flag] Enable description of feature -->
## What
Remove the `:design_management_allow_dangerous_images` feature flag.
## Owners
- Team: ~"group::knowledge"
- Most appropriate slack channel to reach out to: `#f_design-management`
- Best individual to reach out to: @.luke
## Expectations
### What are we expecting to happen?
Users will be able to upload SVG images within design management.
### What might happen if this goes wrong?
There may be a security issue around serving SVGs. Note, the security implications have been addressed in the MR https://gitlab.com/gitlab-org/gitlab/merge_requests/16160 including a sign-off from the security team. However, we want to further assess this in production.
### What can we monitor to detect problems with this?
Work with security to verify that having this feature enabled is safe.
## Beta groups/projects
- `gitlab-org/gitlab` project
## Roll Out Steps
- [x] Enable on staging
- [x] Test on staging https://gitlab.com/gitlab-org/gitlab/-/issues/34279#note_302877400
- [ ] Ensure that documentation has been updated
- [x] Enable on GitLab.com for individual groups/projects listed above and verify behaviour
- [x] Coordinate a time to enable the flag with `#production` and `#g_delivery` on slack.
- [ ] Announce on the issue an estimated time this will be enabled on GitLab.com
- [ ] Enable on GitLab.com by running chatops command in `#production`
- [ ] Cross post chatops slack command to `#support_gitlab-com` and in your team channel
- [ ] Announce on the issue that the flag has been enabled
- [ ] Remove feature flag and add changelog entry
- [ ] After the flag removal is deployed, [clean up the feature flag](https://docs.gitlab.com/ee/development/feature_flags/controls.html#cleaning-up) by running chatops command in `#production` channel
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