[chore] complete and normalize the attributes of engine objects (#6258)

Drop outdated engine attributes: supported_languages, language_aliases

Complete, normalize and document the type definitions for the engine-module and
engine-class.

For the ``engine.about`` section of the configuration, a type check is performed
based on structure ``searx.enginelib.EngineAbout``.

The property ``engine.about.language`` no longer exists; existing values have
been migrated to ``engine.language``.

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

searx/engines/ansa.py

@@ -42,8 +42,8 @@ about = {
     'use_official_api': False,
     'require_api_key': False,
     'results': 'HTML',
-    'language': 'it',
 }
+language = "it"
 
 
 def request(query, params):