Fix deprecation warning by changing `CLIPFeatureExtractor` to `CLIPImageProcessor`.

Hey riffusion 👋,

Your model repository seems to contain logic to load a feature extractor that is deprecated, which you should notice by seeing the warning:

```
transformers/models/clip/feature_extraction_clip.py:28: FutureWarning: The class CLIPFeatureExtractor is deprecated and will be removed in version 5 of Transformers. Please use CLIPImageProcessor instead. warnings.warn(
```

when running `pipe = DiffusionPipeline.from_pretrained(riffusion/riffusion-model-v1)`.This PR makes sure that the warning does not show anymore by replacing `CLIPFeatureExtractor` with `CLIPImageProcessor`. This will certainly not change or break your checkpoint, but onlymake sure that everything is up to date.

Best, the 🧨 Diffusers team.

model_index.json

@@ -3,7 +3,7 @@
   "_diffusers_version": "0.4.0",
   "feature_extractor": [
     "transformers",
-    "CLIPFeatureExtractor"
+    "CLIPImageProcessor"
   ],
   "safety_checker": [
     "stable_diffusion",