docs: fix wikipedia description at https://python.langchain.com/docs/integrations/retrievers/ All retrievers section (#31372)

…integrations/retrievers/ All retrievers section

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docs/docs/integrations/retrievers/wikipedia.ipynb

@@ -17,7 +17,6 @@
       "source": [
         "# WikipediaRetriever\n",
         "\n",
-        "## Overview\n",
         ">[Wikipedia](https://wikipedia.org/) is a multilingual free online encyclopedia written and maintained by a community of volunteers, known as Wikipedians, through open collaboration and using a wiki-based editing system called MediaWiki. `Wikipedia` is the largest and most-read reference work in history.\n",
         "\n",
         "This notebook shows how to retrieve wiki pages from `wikipedia.org` into the [Document](https://python.langchain.com/api_reference/core/documents/langchain_core.documents.base.Document.html) format that is used downstream.\n",