[Job Launcher] Remove legacy CVAT and GCV logic

[flopez7]

Description
Remove legacy CVAT-specific validation and GCV-related logic from Job Launcher create flows

Motivation
This logic belongs to the old job-type-specific flow and makes Job Launcher harder to maintain. Cleaning it up is the first step toward a simpler, manifest-driven creation flow.

Implementation details

• Remove CVAT-specific create-time validation
• Remove GCV-related code and wiring, and delete or simplify create logic that is only needed by the old flow.
• Keep the existing API behavior unchanged.