[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/engines/cppreference.py

@@ -1,37 +0,0 @@
-# SPDX-License-Identifier: AGPL-3.0-or-later
-"""Cppreference"""
-from lxml import html
-from searx.utils import eval_xpath
-
-
-about = {
-    "website": "https://en.cppreference.com/",
-    "wikidata_id": None,
-    "official_api_documentation": None,
-    "use_official_api": False,
-    "require_api_key": False,
-    "results": 'HTML',
-}
-
-
-categories = ['it']
-url = 'https://en.cppreference.com/'
-search_url = url + 'mwiki/index.php?title=Special%3ASearch&search={query}'
-
-
-def request(query, params):
-    params['url'] = search_url.format(query=query)
-    return query
-
-
-def response(resp):
-    results = []
-    dom = html.fromstring(resp.text)
-    for result in eval_xpath(dom, '//div[contains(@class, "mw-search-result-heading")]'):
-        results.append(
-            {
-                'url': url + eval_xpath(result, './/a/@href')[0],
-                'title': eval_xpath(result, './/a/text()')[0],
-            }
-        )
-    return results

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