docs: remove mentions of pydantic_v1 in tutorials (#1709)

docs/docs/tutorials/plan-and-execute/plan-and-execute.ipynb

@@ -238,7 +238,8 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "from langchain_core.pydantic_v1 import BaseModel, Field\n",
+    "# NOTE: you must use langchain-core >= 0.3 with Pydantic v2\n",
+    "from pydantic import BaseModel, Field\n",
     "\n",
     "\n",
     "class Plan(BaseModel):\n",