Python code modernization, 3/n (#1157)

* Remove __metaclass__ = type.

for i in $(grep -REl '__metaclass__ = type' plugins/ tests/); do
  sed -e '/^__metaclass__ = type/d' -i $i;
done

* Remove super arguments, and stop inheriting from object.

plugins/module_utils/_api/context/api.py

@@ -33,7 +33,7 @@ def create_default_context():
     )
 
 
-class ContextAPI(object):
+class ContextAPI:
     """Context API.
     Contains methods for context management:
     create, list, remove, get, inspect.

plugins/module_utils/_api/context/context.py

@@ -28,7 +28,7 @@ from .config import (
 IN_MEMORY = "IN MEMORY"
 
 
-class Context(object):
+class Context:
     """A context."""
 
     def __init__(