tests/lib/pkgdb: curl is already available on AMZN2, AL2023, and CentOS7
Curl is already preinstalled (or provided by other package) in all those images.
Specifically on AL2023, attempt o install curl will trigger a conflict with
curl-minimal like so:
```
Problem: problem with installed package curl-minimal-8.3.0-1.amzn2023.0.2.x86_64
- package curl-minimal-8.3.0-1.amzn2023.0.2.x86_64 conflicts with curl provided by curl-7.87.0-2.amzn2023.0.2.x86_64
- package curl-minimal-8.0.1-1.amzn2023.x86_64 conflicts with curl provided by curl-7.87.0-2.amzn2023.0.2.x86_64
```
Signed-off-by: Maciej Borzecki <email address hidden>
