docs: remove unused imports in Tutorials Basics (#25919)

## Description

- `List` is not explicitly used, so the unnecessary imports will be
removed.

docs/docs/tutorials/llm_chain.ipynb

@@ -479,8 +479,6 @@
     "\n",
     "```python\n",
     "#!/usr/bin/env python\n",
-    "from typing import List\n",
-    "\n",
     "from fastapi import FastAPI\n",
     "from langchain_core.prompts import ChatPromptTemplate\n",
     "from langchain_core.output_parsers import StrOutputParser\n",
@@ -512,7 +510,6 @@
     ")\n",
     "\n",
     "# 5. Adding chain route\n",
-    "\n",
     "add_routes(\n",
     "    app,\n",
     "    chain,\n",

docs/docs/tutorials/retrievers.ipynb

@@ -337,8 +337,6 @@
     }
    ],
    "source": [
-    "from typing import List\n",
-    "\n",
     "from langchain_core.documents import Document\n",
     "from langchain_core.runnables import RunnableLambda\n",
     "\n",