[pitivi] Fix pylint useless-return

[Thibault Saunier <tsaunier src gnome org>]

commit 38ed221f0d17456389abcf2ea8dcd7d7c4d80166
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Fri Oct 25 14:21:05 2019 +0200

    Fix pylint useless-return

 pitivi/effects.py      | 1 -
 pitivi/utils/system.py | 1 -
 2 files changed, 2 deletions(-)
---
diff --git a/pitivi/effects.py b/pitivi/effects.py
index a3af10d6..dd0ff851 100644
--- a/pitivi/effects.py
+++ b/pitivi/effects.py
@@ -629,7 +629,6 @@ class EffectsPropertiesManager(GObject.Object, Loggable):
         self.log('UI is being auto-generated for "%s"', effect_name)
         effect_widget.add_widgets(create_property_widget=self.create_property_widget, with_reset_button=True)
         self._postConfiguration(effect, effect_widget)
-        return None
 
     def do_create_property_widget(self, effect_widget, effect, prop, prop_value):
         """Creates a widget if the `create_property_widget` handlers did not."""
diff --git a/pitivi/utils/system.py b/pitivi/utils/system.py
index 1f6534fa..dd6018e3 100644
--- a/pitivi/utils/system.py
+++ b/pitivi/utils/system.py
@@ -54,7 +54,6 @@ class System(GObject.Object, Loggable):
             icon (str): The icon to be shown with the message
         """
         self.debug("desktopMessage(): %s, %s", title, message)
-        return None
 
     def getUniqueFilename(self, string):
         """Gets a filename which can only be obtained from the specified string.