[Chore]: refactor out unused/redundant params in diffusion pipelines (#1235)

Signed-off-by: Huang, Zeyu <11222265+fhfuih@users.noreply.github.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

docs/contributing/model/adding_diffusion_model.md

@@ -382,7 +382,7 @@ def forward(
         for p in req.prompts
     ]
 
-    # Extract sampling parameters
+    # Extract common sampling parameters
     sampling_params = req.sampling_params
     num_inference_steps = sampling_params.num_inference_steps or 50
     guidance_scale = sampling_params.guidance_scale or 7.5