[fix] logger per engine: make .logger is always initialized

the openstreetmap engine imports code from the wikidata engine.
before this commit, specific code make sure to copy the logger variable to the wikidata engine.

with this commit searx.engines.load_engine makes sure the .logger is initialized.
The implementation scans sys.modules for module name starting with searx.engines.

searx/engines/openstreetmap.py

@@ -438,8 +438,3 @@ def get_key_label(key_name, lang):
         if labels is None:
             return None
     return get_label(labels, lang)
-
-
-def init(_):
-    import searx.engines.wikidata  # pylint: disable=import-outside-toplevel
-    searx.engines.wikidata.logger = logger