Reduce to Sentence Transformers 2.3.1

(Otherwise people will get warnings as 2.4.0 isn't out yet for a few more days)

config_sentence_transformers.json

@@ -1,9 +1,7 @@
 {
   "__version__": {
-    "sentence_transformers": "2.4.0.dev0",
+    "sentence_transformers": "2.3.1",
     "transformers": "4.37.0",
     "pytorch": "2.1.0+cu121"
-  },
-  "prompts": {},
-  "default_prompt_name": null
+  }
 }