Deprecate yaml format for SUSE importer and ingest data in CSAF, OVAL or CVRF format

This reply is from Marcus Meissner from Suse
```
Hi,

FWIW. the backports data in the yaml directory is no longer generated
and I have now deleted the data. Our PM only wishes that we publish data
in standard formats.

As Alexander writes, please use our OVAL, CVRF or CSAF data preferably.

The YAML file with the CVSS scores will stay however for ease of
consumption.

Ciao, Marcus
```

Suse has dropped the support for backport data from the YAML folder, so the suse-backport importer that we were migrating will not be able to import any data. We will drop this importer and write a new importer post-migration for ingesting data from OVAL, CVRF, or CSAF data format.