[mod] podcastindex: remove engine (#6140)

PodcastIndex.org started using a Proof-of-Work JavaScript
challenge whose results are sent as `X-Pow-*` request headers.
Although it is technically possible to re-implement the
PoW challenge in Python, it's likely impossible to maintain
because

- the actual Proof of Concept logic might change very often

- the whole idea of the Proof of Work challenge is to use
  a "big" amount of resources (about 1s on my PC); so executing the challenge
  would almost block all other work on the SearXNG instance

At first glance, the challenge looks very similar to what
Anubis does, because it also uses SHA256 hashes.

searx/engines/podcastindex.py

@@ -1,41 +0,0 @@
-# SPDX-License-Identifier: AGPL-3.0-or-later
-"""Podcast Index"""
-
-from urllib.parse import quote_plus
-from datetime import datetime
-
-about = {
-    'website': 'https://podcastindex.org',
-    'official_api_documentation': None,  # requires an account
-    'use_official_api': False,
-    'require_api_key': False,
-    'results': 'JSON',
-}
-categories = []
-
-base_url = "https://podcastindex.org"
-
-
-def request(query, params):
-    params['url'] = f"{base_url}/api/search/byterm?q={quote_plus(query)}"
-    return params
-
-
-def response(resp):
-    results = []
-
-    json = resp.json()
-
-    for result in json['feeds']:
-        results.append(
-            {
-                'url': result['link'],
-                'title': result['title'],
-                'content': result['description'],
-                'thumbnail': result['image'],
-                'publishedDate': datetime.fromtimestamp(result['newestItemPubdate']),
-                'metadata': f"{result['author']}, {result['episodeCount']} episodes",
-            }
-        )
-
-    return results

searx/settings.yml

@@ -1697,10 +1697,6 @@ engines:
       # image proxy of https://pixiv.perennialte.ch
       # - https://pximg.perennialte.ch
 
-  - name: podcastindex
-    engine: podcastindex
-    shortcut: podcast
-
   # Required dependency: psychopg2
   #  - name: postgresql
   #    engine: postgresql