move prune_config to module level function

mycroft/configuration/config.py

@@ -46,6 +46,20 @@ def is_remote_list(values):
     return True
 
 
+def prune_config(config, prune_list):
+    """Delete list of nested keys from the provided config.
+
+    Arguments:
+        config (dict): config to prune
+        prune_list (list(str)): list of keys to delete. Each item may be a
+                                period separated list of nested keys eg
+                                ["nested.dict.key", "listener.sample_rate"]
+    """
+    for key in prune_list:
+        config = delete_key_from_dict(key, config)
+    return config
+
+
 def translate_remote(config, setting):
     """Translate config names from server to equivalents for mycroft-core.
 
@@ -243,7 +257,7 @@ def load_config_stack(configs=None, cache=False):
                isinstance(config, LocalConf) and config.path == USER_CONFIG:
                 if user_config_disabled:
                     continue
-                Configuration.prune_config(config, protected_keys)
+                prune_config(config, protected_keys)
 
             merge_dict(base, config)
 
@@ -297,9 +311,3 @@ def patch_clear(message):
         """
         Configuration.__patch = {}
         Configuration.load_config_stack(cache=True)
-
-    @staticmethod
-    def prune_config(config, prune_list):
-        for key in prune_list:
-            config = delete_key_from_dict(key, config)
-        return config

test/unittests/configuration/test_configuration.py

@@ -67,7 +67,7 @@ def test_local(self, mock_json_loader, mock_isfile, mock_exists,
         self.assertEqual(lc, {})
 
     def test_prune_config(self):
-        prune_config = mycroft.configuration.Configuration.prune_config
+        prune_config = mycroft.configuration.config.prune_config
         config = {'a': 1, 'b': {'c': 1, 'd': 2}, 'e': 3}
         self.assertEqual(prune_config(config, ['b']), {'a': 1, 'e': 3})
         self.assertEqual(prune_config(config, ['b.c']), {