[del] remove whaleslide (website is down)

Closes #639.

searx/settings.yml

@@ -1536,28 +1536,6 @@ engines:
       require_api_key: false
       results: HTML
 
-  - name: whaleslide
-    shortcut: whale
-    engine: json_engine
-    paging: true
-    # This API Token is needed to work
-    search_url:
-      https://search.whaleslide.com/api/v1/search_v2/web/{pageno}?q={query}&api_token=f8OhUDEYKUICHDnIxEgI7Cb4uYyTBqT4nO8iueNbfTO3devS24yElGqM7nCm
-    url_query: url
-    title_query: title
-    title_html_to_text: true
-    content_query: abstract
-    content_html_to_text: true
-    categories: general
-    disabled: true
-    about:
-      website: https://whaleslide.com/
-      wikidata_id:  # No Wikidata page
-      official_api_documentation: false
-      use_official_api: false
-      require_api_key: false
-      results: JSON
-
   - name: naver
     shortcut: nvr
     engine: xpath