With $wgDisableTextSearch = true and $wgSearchForwardUrl = false MediaWiki search falls back to Google for site searches:
The search engine used (and the entire HTML of the form) can be customized with the searchdisabled and googlesearch messages, but it seems unusual that MediaWiki would include a proprietary service like this as default (albeit as a fallback).
We could use DuckDuckGo instead, or any other privacy-preserving search engine, but removing the feature may be more sensible.

