[IMPR] Filter does not have to be subclassed

Any instance can be passed which has a filter method with the same
semantics:
https://docs.python.org/3/library/logging.html?highlight=logging%20filter#logging.Filter

This also solves an deepsource PY-A6006 issue.

Change-Id: Ic2d3c345725ed33809c484be709f0c3d8b282149

pywikibot/userinterfaces/terminal_interface_base.py

@@ -608,12 +608,12 @@ def emit(self, record) -> None:
         self.UI.output(msg, targetStream=self.stream)
 
 
-class MaxLevelFilter(logging.Filter):
+class MaxLevelFilter():
 
     """Filter that only passes records at or below a specific level.
 
-    (setting handler level only passes records at or *above* a specified level,
-    so this provides the opposite functionality)
+    .. note:: setting handler level only passes records at or *above* a
+       specified level, so this provides the opposite functionality.
 
     """