[Clean] Remove multi-replica Bagel CI and related docs/configs (#3407)

Signed-off-by: Chenguang ZHENG <645327136@qq.com>

benchmarks/diffusion/README.md

@@ -32,8 +32,6 @@ python3 benchmarks/diffusion/diffusion_benchmark_serving.py \
 
 - The benchmark talks to `http://<host>:<port>/v1/chat/completions`.
 - If you run the server on another host or port, pass `--base-url` accordingly.
-- To compare diffusion multi-replica serving, restart the server with different
-  `runtime.num_replicas` values and keep the benchmark parameters unchanged.
 
 ## 2. Supported Datasets
 
@@ -95,35 +93,6 @@ You can point to your own trace using `--dataset-path`.
 
 ## 3. Benchmark Parameters
 
-### Multi-replica sweep
-
-For replica scaling, use the same model, prompt count, image/video size, and
-step count for every run. Change only the serving stage config:
-
-```yaml
-runtime:
-  devices: "0,1,2,3"
-  num_replicas: 4
-```
-
-Then run a fixed benchmark and write one JSON file per replica count:
-
-```bash
-python3 benchmarks/diffusion/diffusion_benchmark_serving.py \
-  --base-url http://localhost:8099 \
-  --model Qwen/Qwen-Image \
-  --task t2i \
-  --dataset random \
-  --num-prompts 32 \
-  --max-concurrency 8 \
-  --request-rate inf \
-  --num-inference-steps 10 \
-  --width 512 --height 512 \
-  --output-file diffusion_replica_4.json
-```
-
-Repeat for `num_replicas=1`, `2`, `3`, and `4`, using matching `runtime.devices`.
-
 ### Basic flags
 
 - `--base-url`: Server address (the script calls `.../v1/chat/completions`).