[V0 deprecation][P/D] Deprecate v0 KVConnectorBase code (1/2) (#21785)

Signed-off-by: Linkun Chen <github@lkchen.net>

.buildkite/test-pipeline.yaml

@@ -749,7 +749,6 @@ steps:
   # this test fails consistently.
   # TODO: investigate and fix
   - VLLM_USE_V1=0 CUDA_VISIBLE_DEVICES=0,1 pytest -v -s test_sharded_state_loader.py
-  - VLLM_USE_V1=0 CUDA_VISIBLE_DEVICES=0,1 pytest -v -s kv_transfer/test_disagg.py
   - CUDA_VISIBLE_DEVICES=0,1 pytest -v -s v1/shutdown
   - pytest -v -s models/multimodal/generation/test_maverick.py