Remove outdated content related to conversation history variables

Author: Riskey

en/use-dify/nodes/llm.mdx

@@ -102,18 +102,12 @@ When processing images, you can control the detail level:
 - **High detail** - Better accuracy for complex images but uses more tokens
 - **Low detail** - Faster processing with fewer tokens for simple images
 
-The default variable selector for vision is `sys.files` which automatically picks up files from the Start node.
+The default variable selector for vision is `userinput.files` which automatically picks up files from the User Input node.
 
 <Frame caption="File processing with multimodal LLMs">
   <img src="https://assets-docs.dify.ai/2024/11/05b3d4a78038bc7afbb157078e3b2b26.png" alt="File Processing" />
 </Frame>
 
-For conversation history in completion models, insert conversation variables to maintain multi-turn context:
-
-<Frame caption="Using conversation history variables">
-  <img src="https://assets-docs.dify.ai/dify-enterprise-mintlify/en/guides/workflow/node/b8642f8c6e3f562fceeefae83628fd68.png" alt="Conversation History" />
-</Frame>
-
 ## Jinja2 Template Support
 
 LLM prompts support Jinja2 templating for advanced variable handling. When you use Jinja2 mode (`edition_type: "jinja2"`), you can: