DDEV-Live needs to delete its backups after pulling to avoid quota trouble

[rfay]

The Problem/Issue/Bug:

• DDEV-Live recently implemented quotas, including quotas on backups of db and files
• ddev-live-client was updated to v0.6.0 in v1.15.2+, and its syntax for deleting database backups has changed.
• The test user that runs tests (and perhaps people who use backups) could easily run out of quota on backups because ddev pull doesn't clean them up.

How this PR Solves The Problem:

• Make sure both files and db backups are deleted after we pull them.
• Adjust code to the new ddev-live delete backup syntax

Manual Testing Instructions:

Just review ddev-live list backups or ddev live list backups after tests have run. There should be nothing there.

Automated Testing Overview:

Related Issue Link(s):

Release/Deployment notes: