[Feature Flag] Remove design_management_reference_filter_gfm_pipeline

What

Remove the :design_management_reference_filter_gfm_pipeline feature flag

Owners

• Team: ~"group::knowledge"
• Most appropriate slack channel to reach out to: #g_create_knowledge
• Best individual to reach out to: @alexkalderimis

Expectations

What are we expecting to happen?

The feature is currently enabled in production, so nothing

What might happen if this goes wrong?

Design references could stop working.

What can we monitor to detect problems with this?

Sentry and bug reports

Roll Out Steps

• Enable on staging (/chatops run feature set feature_name true --staging)
• Test on staging
• Ensure that documentation has been updated
• Enable on GitLab.com for individual groups/projects listed above and verify behaviour (/chatops run feature set --project=gitlab-org/gitlab feature_name true)
• [-] 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 (/chatops run feature set feature_name true)
• [-] Cross post chatops Slack command to #support_gitlab-com (more guidance when this is necessary in the dev docs) 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 by running chatops command in #production channel