This analyzers helps prevent issues when you try to delete an active flow.
Note: With the release of Winter '19 (v44 of the metadata API), Salesforce have made major changes to how Flow and Flow Definitions are handled by the metadata API. See our support doc on the changes and how they affect you.
What triggers this problem analyzer?
If you've included flow deletions in your deployment and those flows are active in the target.
What problem is it solving?
It's not possible to delete active flows. You'll need to deactivate first. If you try to do this using the metadata API, your deployment will fail.
How does it work?
The analyzer will remove the deletions from the deployment. You'll need to deactivate them before you can delete them.