Remove useless line of code from sql.ipynb (#12906)

This PR remove a single line of code from a notebook of the
documentation. This line used to define a variable, which is never used
in the code.
For further context, for reviewers, here is the online documentation:
https://python.langchain.com/docs/use_cases/qa_structured/sql#case-3-sql-agents

docs/docs/use_cases/qa_structured/sql.ipynb

@@ -524,7 +524,6 @@
     "from langchain.agents.agent_types import AgentType\n",
     "\n",
     "db = SQLDatabase.from_uri(\"sqlite:///Chinook.db\")\n",
-    "llm = OpenAI(temperature=0, verbose=True)\n",
     "\n",
     "agent_executor = create_sql_agent(\n",
     "    llm=OpenAI(temperature=0),\n",