[fix] engine - cppreference has no longer a search function (#5273)

cppreference has replaced its search (``mwiki/index.php?title=``) with a DDG
search.

The engine was first introduced in SearXNG with PR-3274 [1], and even back then
the mediawiki proved to be incompatible, which is why the API could not be used
at the time. Now there isn't even a dedicated search function anymore.. I think
the cppreference project suffers from a lack of maintenance.

[1] https://github.com/searxng/searxng/pull/3247

Closes: https://github.com/searxng/searxng/issues/5271

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/settings.yml

@@ -665,12 +665,6 @@ engines:
     api_key: ""
     inactive: true
 
-  - name: cppreference
-    engine: cppreference
-    shortcut: cpp
-    paging: false
-    disabled: true
-
   - name: crossref
     engine: crossref
     shortcut: cr