[del] remove searx_engine - no use case (#6680)

There is no meaningful use-case for the engine, moreover the implementation
is 10 years old (formerly searx) and no longer fits the current data model of
SearXNG.

Closes: - https://github.com/searxng/searxng/issues/6676

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

searx/settings.yml

@@ -2296,14 +2296,6 @@ engines:
     shortcut: pwv
     disabled: true
 
-  # - name: searx
-  #   engine: searx_engine
-  #   shortcut: se
-  #   instance_urls :
-  #       - http://127.0.0.1:8888/
-  #       - ...
-  #   disabled: true
-
   - name: seekninja
     engine: seekninja
     shortcut: sen