docs: remove unnecessary setup from tutorial (#31445)

Author: ccurme

docs/docs/tutorials/llm_chain.ipynb

@@ -115,10 +115,6 @@
     "    )\n",
     "    if not os.environ.get(\"LANGSMITH_PROJECT\"):\n",
     "        os.environ[\"LANGSMITH_PROJECT\"] = \"default\"\n",
-    "if \"OPENAI_API_KEY\" not in os.environ:\n",
-    "    os.environ[\"OPENAI_API_KEY\"] = getpass.getpass(\n",
-    "        prompt=\"Enter your OpenAI API key (required if using OpenAI): \"\n",
-    "    )\n",
     "```"
    ]
   },