docs: remove preview warning from partial ordering mode sample notebook (#1986)

Author: tswast

notebooks/dataframes/pypi.ipynb

@@ -48,7 +48,6 @@
    "source": [
     "import bigframes.pandas as bpd\n",
     "\n",
-    "# Preview feature warning:\n",
     "# Use `ordering_mode=\"partial\"` for more efficient query generation, but\n",
     "# some pandas-compatible methods may not be possible without a total ordering.\n",
     "bpd.options.bigquery.ordering_mode = \"partial\""