feat(dbsync snapshot): Remove GVC and DRep functionality from importer | NPG-000

[saibatizoku]

Description

Removes GVC integration and DRep functionality from the DBSync snapshot importer.

This removes DRep-related command-line arguments.

Closes #646

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[jmgilman]

LGTM