Do not add original user message to knowledge search queries for offline chat

It's not required anymore. The extracted questions by the offline chat
model being used should be good enough.

src/khoj/processor/conversation/offline/chat_model.py

@@ -94,7 +94,6 @@ def extract_questions_offline(
         logger.warning(f"Llama returned invalid JSON. Falling back to using user message as search query.\n{response}")
         return all_questions
     logger.debug(f"Extracted Questions by Llama: {questions}")
-    questions.extend(all_questions)
     return questions