Remove `core` folder

[kerthcet]

This is how the code tree looks like right now:

├── api
│   ├── core
│   │   └── v1alpha1
│   │       ├── groupversion_info.go
│   │       ├── model_types.go
│   │       ├── types.go
│   │       └── zz_generated.deepcopy.go
│   └── inference
│       └── v1alpha1
│           ├── config_types.go
│           ├── groupversion_info.go
│           ├── playground_types.go
│           ├── service_types.go
│           ├── types.go
│           └── zz_generated.deepcopy.go

However we do not need the core folder, this is just because a bug of code-generator, which is fixed in https://github.com/kubernetes/kubernetes/pull/125162, we should remove the folder once kubernetes v1.31 is released.

[kerthcet]

/kind bug /priority important-longterm

[kerthcet]

/remove-kind bug /kind cleanup

[kerthcet]

/triage accepted