TP: fixes bug with delivery service requests when deleting a ds

[mitchell852]

What does this PR (Pull Request) do?

• This PR fixes Deleting a DS via a DS request/fulfill immediately does not remove DS from the DS table #4192

The bug was never documented (obviously) so no documentation to fix.
DSRs are not under test.
No change log entry required.

Which Traffic Control components are affected by this PR?

• Traffic Portal

What is the best way to verify this PR?

• Enable delivery service requests (dsRequests.enabled=true) in traffic_portal_properties.json and set overrideRole=admin
• Launch TP
• Login as an admin
• delete a delivery service and select "fulfill immediately"

You will be directed back to the delivery services page and your delivery service will be gone. You can also verify that a delivery service request was created and closed/completed under https://tp.domain.com/#!/delivery-service-requests

If this is a bug fix, what versions of Traffic Control are affected?

• master (0b02a3c)

The following criteria are ALL met by this PR

• This PR includes tests OR I have explained why tests are unnecessary
• This PR includes documentation OR I have explained why documentation is unnecessary
• This PR includes an update to CHANGELOG.md OR such an update is not necessary
• This PR includes any and all required license headers
• This PR ensures that database migration sequence is correct OR this PR does not include a database migration
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

[asf-ci]

Refer to this link for build results (access rights to CI server needed):
https://builds.apache.org/job/trafficcontrol-PR/4926/