Remove pages_migration_mark_as_not_deployed feature flag

What

Remove the :pages_migration_mark_as_not_deployed feature flag

Owners

• Team: relase
• Most appropriate slack channel to reach out to: #gitlab-pages
• Best individual to reach out to: @vshushlin

Expectations

What are we expecting to happen?

Nothing will happen unless we run the specified rake task

What might happen if this goes wrong?

Some projects containing pages may be marked as "not deployed", which will make pages unavailable.

What can we monitor to detect problems with this?

Roll Out Steps

• Confirm that QA tests pass with the feature flag enabled (if you're unsure how, contact the relevant stable counterpart in the Quality department)
• Enable on staging (/chatops run feature set pages_migration_mark_as_not_deployed true --staging)
• Test on staging
• Enable on GitLab.com by running chatops command in #production (/chatops run feature set pages_migration_mark_as_not_deployed true)
• 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

Rollback Steps

• This feature can be disabled by running the following Chatops command:

/chatops run feature delete pages_migration_mark_as_not_deployed