Remove support for and all references to manifest/schema1

[chengfang]

Is your feature request related to a problem? Please describe.

github.com/distribution/distribution/v3/manifest/schema1 package (https://github.com/distribution/distribution/releases) has been deprecated and then removed from distribution/distribution module. In image-updater, there are several places that still use it. In order to bypass lint check, these places are annotated with //nolint:staticcheck. Once we upgrade to newer version of distribution/distribution module that no longer contains this package, these files will no longer compile.

• pkg/registry/client.go
• pkg/registry/client_test.go
• pkg/registry/registry_test.go
• pkg/argocd/update_test.go
• registry-scanner/pkg/registry/client.go
• registry-scanner/pkg/registry/client_test.go
• registry-scanner/pkg/registry/registry_test.go

Describe the solution you'd like
Remove support for schema1 API and features, and remove all references to it from image-updater code base.

Describe alternatives you've considered
keep using the current version of distribution/distribution module, and unable to upgrade.

Additional context